Perriman can fight and magically heal, so he's pretty good as followers go. He will divulge the location of Tulla at the proper point in the storyline. Sebastian can fight, throw, and make lvl 4 Electrical and Explosives items, so he's a very good follower, especially if you still need ways to make money or those items that late in the game. (I often edit him so he makes lvl 7 items when he is high level.) Unless you have a magic-oriented party, Sebastian's far better overall.
yeah sebastion can make you a lot of money in the explosives he can make.........just don't let him throw anything, he starts a lot of fights with your followers. Just let him make the stuff then get it out of his inventory. Give him lots of bullets also. He misses alot! Perriman is just another dante and dante is free! If you got dante way back at lvl 12 then he is way higher in lvl than Perriman is at that time. Parmanian