Luna and ghost panther hands down. They both hit like a truck, Luna will get a uni next update probably throwing her into the top meta, and ghost panther has the best supportive t2 passive.
Luna and 2099 are the best. Not sure where sentinal lands on that list but considering Luna is getting an upgrade i would say shes the best choice.
Ironheart is nothing special
carnage is the worst
because he NEEDS his tier2 to be useful where as characters like luna and 2099 are beasts even at tier1