King Hassan vs Merlin?

Hmmm. A lot of people are going to be rolling for both so you can always use supports for the one you don’t pick.

Everyone around here knows I’m extremely biased about this but I say Merlin

He is the Lord of Memes

If you're purely considering gameplay, Merlin. The answer will always be Merlin. Strong support > everything else in this game. But mate, real talk, just roll for what you want most. It doesn't make enough of a difference to matter, especially with those two. Each have their advantages over the other.

Favorite servants > Everything else

Merlin for gameplay

King Hassan for favourite.

Both are broken.
Grandpa is broken. Some challenge quest 1 year later that Cu alter and Herc cannot do the solo, but he can do.
But Grandpa's broken is like a servant in perfect combination of both tanky+DPS, then you can rely on him as an durable hitter constantly contribute damage. HE IS GRAND ASSASSIN. But still, he possessed somehow weakness, specifically limited to class disadvantage (lower basic damage modifier and mediocre for star adsorption) and hard to manage critical stars if CE is not appropriate.

However, Merlin's broken is....almost everything. People often meme that all servant with Buster orientation could be 100% improved by Merlin. Like Musashi, in fact I dont think Musashi is superior than Okita, but it just make me feel Merlin's existed helped Musashi become the best saber, and Skadi only came 1.5 years later for saving Okita. Also OG Shishou's top performance could be surpassed by Brynhildr and Karna later on.

Merlin's OP is not only for as a critical damage support for Buster hitter, but also for multi-direction complexes support. Like his 2nd skill is better than David and cover more ass than our reliable Mashu. Although 7 turn cool down is a bit high, but with dual Merlin you can save your team's ass again 3 NPs in >8 turns, before multi HP boss came out (>2), normally with dual Merlin you dont need to finish a battle longer than 8 turns. Boss' normal damage could also be recovered by 5000-10000 hp overall for all the team from one Merlin's NP.

And Merlin can build up snowball effect of his NP, due to OP 5 TURN LASTING. Because of that, Merlin is also compatible with some art team, although his most notorious 3rd skill may not be so effective in an art team, but still OP overall. Like Vlad+Tamamo+Merlin team, we all know Tamamo is the engine of art team, but her NP gain is mediocre. However, every servant's NP gain could be doubled up by critical (dual 2030 + Merlin's NP = 21-26 stars, Vlad wont adsorb too much). So both Merlin and Tamamo's art boosting could be improved. Meanwhile once Merlin's first NP activated first, 5% NP charge for team in 5 turn > Waver's 1+2 skill charge effect, let along 1st skill 20% charge for all but only 5 cool down.
What does it means? it means that Tamamo's critical art card as the 3rd place of art chain can receive 43-69% NP gain (the difference of 25 is +5% by Merlin's NP and +20% by Merlin's 1st skill) in a single turn, and Merlin may receive ~73% NP gain (or additional 25-37.5% due to Tamamo's NP oc1-3). This just account for one Merlin NP released, how about spam Merlin's NP? Remember, 5 turn lasting. It is not bad in comparison with Tamamo+Waver art team combo, right?

That is also why some people Meme that Merlin's come kill the quick team. Because 2030 Merlin finished lots of quick card oriented servants' star generation job, provide much much more support for both offensive and defensive, and won't adsorb too much star. It is necessary to use any quick card for low damage? Merlin: NOOOOOO. Only Skadi could bring the glory back to Quick team, but we have to wait very long and meet very changeable events and quests during that.

So you can see why Merlin is OP. I didn't even talked too much about his 3rd skill as for Buster oriented Servants. Like NP1 Lv90 Jalter's NPAAe can deal 150000+200000+230000+16000 damage to normal servants if all buff restored by dual Merlin and herself.

My second account is saving for Merlin+Rin. But right now I just think I can use other SSR archer than Rin, but I cannot lack of Merlin. Like Emiya, Rama, SaberLiz as SR will worked as SSR in the present of 4060 Waver+Merlin. Gil, Ozy, Karna, Quetzalcoatl + dual Merlin = OMG, WTF?