my opinion of each character's assist, if you disagree please provide a counterpoint or an example
good assists:
Polymar - great to keep opponent on lockdown/mixup/extend combos
Roll - extend combos, pressure and leave a puddle that can otg? yes please
Ryu - everyone's favorite assist, and its just so simple
Jun - can be used like Ryu or Morrigan with the added benefit of setting an explosive so she can do extra damage when you tag her in
Karas - lots of stun and can relfect a few projectiles
Tekkaman - great for setups and is bad news for giants
Morrigan - a Ryu alternative
Casshern - anti air assist that can also extend OTG combos, also can hit with the rear of the hitbox
Megaman - anti air assist that does enough hitstun to let some slow supers hit, also allows for juggles
decent assists:
Chun - similar to megaman, but lasts for a shorter period of time
Batsu - just okay, similar in usage to Chun/Mega
Ken - this is whatever, if it came back it would be much nicer
Zero - the game's best assist for pure anti air, works like MvC2 Ken, but is hard to use to extend combos.
Ippatsuman - good for pressure
Alex - good for pressure
Soki - also good for pressure, and has super armor to keep counter attacks in check
Doronjo - really underrated, like a Karas assist that travels, downside is slow speed
Blade - just another AA assist (someone let me know if this has special properties)
bad assists (or if not bad, then very situational):
Yatter 1 - only hits in a specific area
Condor - kinda weak for an anti air imo
Viewtiful Joe - situational, can be used in a few setups but mainly to induce fear
Saki - I think this is debatable, I just haven't seen that much use for it yet
Frank - also debatable, does stagger for a bit and hit full screen but seems limited in usage sometimes
undecided: Yatter 2, but it seems like her's is pretty solid