Prison Tower Challenge Quest DPS?

Since you have your own merlin and jalter you could go full buster memes and just do merlin, merlin, jalter which I know someone has done a video of it succeeding and the servants weren't high on np or skill level, really.

I suggest looking at the final guide for that quest as it suggests a lot of comps centered around dps and based on what is in the match. I specifically remember it suggesting a saber as the main dps for the reason that the fight has no archers. There's a lot of ways you can take it and you have the 2 best supports in the game so you have a lot of wiggle room in making a viable team that can stay alive.

Gil is a pretty good option. Almost every servant is weak to his NP, and Merlin and Waver, plus his own buffs, will make him extremely deadly for everything except the rulers and the two lancer mobs in round 5.

JAlter wouldn't have to worry about anyone resisting her damage, and the heals from Merlin could (potentially) offset the demerit on her third skill.

Herc I wouldn't recommend as much- I plan on using mine as a last resort with his bond CE, but don't want to use him with others. That restricts the use of his buster chains and guts.

If you have a friend with a good Mama Raikou, she'd fit in nicely too. Main weakness is her staying alive (but Waver has defense up and Merlin has invincibility) and her not having a crit damage buff (again, Waver and Merlin both provide).