If you can have only one pt 2: Gilgamesh Vs Ishtar!

My vote is for Gilgamesh. He's such a pompous ass, it's hard not to enjoy hearing his interactions and opinions.
Going back to skills, I like how ishtar has a NP charge of up to 50% and a high chance for invulnerable so higher chance of surviving a NP without relying on a different servant like Gilgamesh has to do. I find Gilgamesh is designed to take all critical stars, hit hard, charge his NP bar quickly as a result of his skills collectively and be able to use his NP again fairly promptly. This is before supports.
Finally and most importantly in regards to your question, with most servants being weak to Enuma Elish, Gilgamesh can be used more effectively in tough fights with servants that aren't just sabers.

I'm no guru with stats here, and also don't have both, so I'm purely commenting from play experience with support list.
I think I would go for Gil in this instance. Not to mention about the extra damage from his NP, I think overall Gil gives me a more consistent performance.
Ishter does provide some nice utilities, but they slap an 80% random chance on to it, which might fail when you most wanted it, therefore you need to bring someone like Ozy along to make sure you get 100% activating chance. Secondly, you really need to know how to time Ishter's 3rd skill and foresee the situation, because the next set of cards might not work in your favour.
For fun or trolling wise, I like to play with Ishter more, but for other quest type challenge I would rely on Gil

This one is tough for me. Both have similar skills, both hit hard, and both are AoE. Oof.
One thing against Gil is that he doesn't have anything for survival (no defense buff, no evade, nothing), so an enemy NP can kill him off if you're unprepared. Ishtar at least has some sort of survival kit. Granted, it's chance-based invincibility, so it has a possibility of failing when you need it the most.

In terms of damage, Gil does have a slightly higher attack than Ishtar. Plus, he has a star gathering skill so crits will be abundant.

It's a tough choice, but I'm going to have to go with Gil. I guess the deciding factor is his anti-servant NP which can really pull your team through those hard boss battles. But, if I ever got either one of them, I would be equally happy.

These servant vs. servant questions are very interesting. Thanks OP for coming up with it. I love reading what other people think.

Have to go with Gilgamesh. I've always enjoyed him as a character whereas I'm a bit partial to Tohsaka. Character traits aside, Gilgamesh has always had a top spot among the 5-star servants and for good reason. His offensive potential for a non-avenger, non-berserker is unmatched, being a top tier pick in JP and NA since launch. The bonus damage against servants makes him invaluable.

Ishtar basically does all the same stuff but lacks the bonus damage against servants, making her less useful in that capacity.

I would go for Gilgamesh, if i use him then it's going to be an all out battle. For now i use Ishtar a lot, because my Gil are already reached his max Bond.

Short introduction, one the most dominant factor of both Archers :
5 Buster and 5 Art and 5 Quick and 8 Extra, stupid hit count for each cards and 8 hit counts for extra attack. Gilgamesh can quite generate the Crit stars for himself and fill his NP gauge pretty fast with that.

Since both are monsters of gameplay, including Tesla then i would choose anyone between the 3 monsters.
I also put Tesla because he only lose in terms of popularity but in terms of gameplay, Tesla is pretty much equal to Gil and Ishtar.

For the stats, the difference is not too big and i would say their stat is similiar.

Burst damage capability :
- NP damage, non-servant it's Ishtar and for servants it's Gilgamesh and Tesla.
- Buster Crit, the winner is Ishtar followed by Gilgamesh on the 2nd slot and Tesla on the 3rd slot.
NP gain :
- Ishtar can use her NP on demand with a CEs like Golden Sumo or HNS. She guaranteed nothing for NP refund after she use her NP. Only have 50 % NP battery, no NP gain skills.
- Tesla is the best between the 3 archer monsters, NP gain + 50 % skill for 3 turns and instant NP battery + 50 %. Instant NP, refund NP and after that he can use his NP again, this guy is a beast.
- Gilgamesh, second only to Tesla. NP battery 30 % and NP gain 50 % for 3 turns. A bit below Tesla, pretty much almost the same.
Buster Crit Consistency :
- Gilgamesh high hit count for each cards and tremendeous star gen is a way to describe this.
- Ishtar, below Gilgamesh in terms of Crit Consistency. Only a bit above Tesla, not really different.
- Tesla, he rekt things hard and can crit pretty hard but the least consistent between the 3 archer.
Survivability :
- Tesla, guaranteed guts with 5 turn CD along with Def Up + 30 %. The total winner of this category. His NP can also has a chance to stun his enemy, 30 % chance to stun and 80 % to gain def up buff.
- Ishtar, at least she has a 1 turn Invincibility. 80 % chance to gain Invincibility.
- Gilgamesh, only thinks about damage and damage and damage. No survivability, like mentioned before he's pretty selfish.

For tactical and survivability, Tesla wins.
For Consistencies, Gilgamesh wins.
For normal card burst, Ishtar wins.

Like mentioned before, they're the best when doing their job. Each monster have their weakness and strengths so if i got one, gameplay wise then i'm fine with an Ishtar, Tesla or Gilgamesh.

Bonus : here i hope DW can buff and strengthens servant like Arjuna.

I'll go for Gil cuz of broken NP against servants and the ability to screw anyone (except lancers probably) with 2 Merlin /w 2030 ce and NPBB crit chain.
Ishtar's unique Mana Burst skill (tho good and heavenly 3turn cd) might not turn into her favor especially when you're going for an NPBB chain or any NPXX brave chain only to see that none of her cards or only 1 (and its not buster :x) is available and potentially waste a turn of the 2 Merlin's buster buffs. Her defensive skill which is tied to her battery have a good success rate tho relying on it might screw you if you don't have any back ups for it.

Both are great but I'll pick Ishtar for 2 reasons:
1. Survivability and better NP battery + crit dmg.
2. Her skillset is just screaming "SPOILED GODDESS", you can feel it in the gameplay cause she NEEDS your attention. It's very fun.
Also, waifu reasons :)

Very late of me, (sumanai) but I figured I'd offer my own opinions on some of the older debates, if that's alright with you.

These two are top-tier as AoE Archers, and both can utterly annihilate any wave of enemies with a single blow, but their edges differ just enough that one surpasses the other.

Ishtar boasts incredible potential for damage and her three skills are focused on just that. Her first skill is like Charisma, but slightly buffs crit damage, and her NP charging skill comes with the chance to give her Invincibility and Ignore Invincibility, and her Mana Burst can increase her own attack by 50% at the max. Her NP has the overcharge effect of boosting her Buster cards, making her Buster chains utterly devastating with the proper conditions. Despite this, her Mana burst delay can lead to unpredictable RNG fails if Busters fail to show and her defensive skills are RNG-based as well. She may stay alive for quite a while, but unlucky misses can hinder her optimum performance.

Gil is an absolute beast of a servant, and has the power to show it. Charisma boosts his team's damage, and his Golden Rule skill improves his NP gain. His third skill boosts his already high star absorption as an Archer, and has the side effect of giving him an NP boost. His damage output ranks near the highest in the game, and his NP has the unique niche of being able to demolish nearly any Servant. Additionally, he can fill his NP meter quickly with two NP-based skills and high hit counts and he can chain his NP with his Buster Cards, boosting his absurd damage even further. His disadvantages would probably lie in that his NP's niche is less useful when facing bosses that normally appear alone, in which case an ST NP would normally be better, and that he has little to no defensive skills and must be supported by his team, given he loses health quickly before he can defeat his enemies.

Overall, Ishtar may be very powerful, but Gilgamesh simply is able to outperform her in her specialties and boasts a higher capacity for destruction. Ishtar may be a top-tier farmer, but Gilgamesh can compete with her in her own field and outclass her against challenging bosses.