Roll for Jalter?

For someone who has both jalter and raikou i would say dont roll for except you really want her. I mainly use raikou in boss battles and farming. Both of them have the same role but jalter isnt as selfish as raikou.

Those two don’t serve the exact same rolls. Jalter is a single target buster NP while Mama is an AOE. So Jalters NP can do far more damage to a single enemy that mama can. Against a Beserker boss there is no one better. She is also much more survivable than Raikou is thanks to her Avenger class vs beserker.

Jalter also has a better team skill set thanks to her attack boost being team wide and also giving any servant with the dragon trait an extra attack buff. Thanks to her Crit Damage up skill she is also a better buster crit servant. They both have their invincibility ties to their buster buffs which is a pain, but at least it’s still there. I have Jalter and am glad I rolled to get her to NP2 for the extra damage boost. She will be one of the best servants paired with Merlin too.

I’d also take a look at your friends list. If you have a bunch of people with powered up Jalters you could feel a little better passing her up and saving for Merlin. Of course, you can be certain Merlin will be all over your friends list as I think a ton of people are going to be breaking the bank for him. I wouldn’t say rolling for Jalter is just a matter of preference. She is a harder single target hitter than Raikou and more survivable. You will probably end up using Raikou more but in the situations where Jalter shines, she really shines. Hope this helped a bit

Raikou hit real hard, from gameplay aspect she's strong enough to fill a lot of your needs.
I mean you use her everyday on the the farm section, event clearing, free quest, and can beat boss easily.

Some example here, i use Gilgamesh which is pretty similiar to Raikou in the gameplay.
Being AOE doesn't mean he and she can't hit hard. Both is a Premiere Buster Crit to begin with, we don't depend on NP so much there are a lot of Buster Crit servant with their own playstyle.

AOE Gil? I kill Raid Boss in average of 4 turn and 2 turn is my best yet ( RNG help ).
AOE Raikou? Never seen Raikou damage then? I borrow friends Raikou and she deals tons of damage too, Those Raid Boss is just obliterated similiar to Gil in result.
AOE again? Gil and Raikou hit's like a truck, using them to clear Nerofest Grand Finale and it is a joke.
I even close my app, because no challenge using those Monster.
Camelot? Raikou smurfing there, like it's nothing.
Raikou is AOE but she can 1 turn OHKO a lot of bosses.
Gilgamesh is AOE but he can 1 turn OHKO a lot of bosses.

It's up to us, how we play, how we support them, when is the right time of using those Mystic Code and also we know our enemy. Even 1-3 Star can beat FGO.

Servant like Jalter, Raikou, Ozymandias, and Gilgamesh is just another example of Broken servant, just pick your favorite between these Premiere monster and then you're set.

What is the use of comparing them really? It's like comparing Waver to Merlin, they have different kit but still FGO cheat engine.

Merlin is one of the best servant to roll, as he is like a best friend to Jalter and Raikou.
It's up to you, whatever you choose still gives you win-win situation.