I like both planes, but there are a couple things that set them apart.
Brewster:
Very good plane in terms of turning, if I'm not mistaken, can out turn a Hurri or a zeke, but I haven't found that out yet. No WEP, just like the I16, but it still climbs well. Not to much of a stall, even when flaps are extended. Only downfall of this plane is it's poor guns. You can put a 3 second burst on a plane and not kill it. Takes a lot to kill some thing in it. All in all, very good Early War/Mid War fighter plane, can see why then Eny is at 25.
I16:
Becoming one of my favorite planes in the game, and cannot see why it's at 30 ENY. Although it is an early war fighter, it can stand with a lot of good fighters. Great climb, excellent guns (20mm package), and good turner, not going to say the best. Were it hurts is at it's stall characteristics. Even if you have some speed in a turn fight, you can still stall it pretty bad. I like to call it a pancake stall, but it is pretty easy to get out of, as long as you have at least 800ft.
IMO, even though it has the pancake stall, I16 is my favorite between the two, easy to kill something in it, and fun to fly. I16 my new favorite plane.