Best staff??

The mounted healers are generally considered the most versatile. Genny has Wrathful Staff so, out of the box, she's the best offensively.

mounted healers like Clarine and Priscilla for higher mobility, but the rest is subjective really. staffs can debuff the enemy units or deal damage.

My preference is Clarine w/pain staff and rehabilitate, but as a whole I find healers take up a slot on the team and don't help against most of the meta's orko sweepers so unless I was running a wall, I'd take a dancer with secondary healing

I like Wrys. Our father only needs heals to be good! Joking aside, Clarine and Maria, they are my two favorite FE staff users.

Clarine is the best staff user because she's on a horse, she has decent speed, res and atk and she can be easily merge because she is available at 5 star rarity. If the last thing is not an issue, Elise is the best

Depends.

Offensive: with Wrathful staff: Genny and Lucius are good. Elise with horse buffs is probably the best atm, but none of them are great tbh. We will eventually get a very good offensive staff

For wall support: there are a lot, basically u want to focus on one stat or both def and res. With fortress, and live to serve2 as B slot and pain as the weapon. For both res and def I can think of sakura. For res wrys is a mosnter, for def only Azama is pretty good.
Clarisse can be amazing if u merge her up as she has a great spd, good res, not so good but workable def. She is also mounted which makes her even better.