D11 is actually slightly faster than the D25 and D40 and significantly faster than the N on MIL power. It's still faster than the D25 on WEP as well as matching the D40! I hear people saying they don't like the D11 because it's so slow, yet it's the 2nd fastest Jug on MIL power!

I think the M is the easiest to get in and dogfight with. Great engine power, good climbing ability and the exceptional diving ability, and a respectable turn rate that can be helped with a little flap work as well. All of the Jugs are actually pretty ok in a stall fight as well as long as the fight doesn't go vertical for too long.
D11 I say is the next best dogfighter. It's the lightest of them all, 2nd fastest on MIL power, ok climb rate, it's a jug so it dives like no other (I caught a P-38L in this plane the other day!), and it's got a superb turning ability that not many know of. The D11 is very stable in a stall fight and can give spitfires trouble sometimes! The only thing that makes this thing a bit tougher to use than the M is the canopy framework and razorback design. I personally don't mind it but some people seem to hate it.
D25 and D40 are virtually the same plane as far as I can ever tell. They weigh the same, seem to turn the same, climb the same, and have the same speed. The difference is the WEP. The D40 has better WEP than the D25. These two planes may have an upgraded engine from the D11, but they are heavier too and that's what makes them slower on MIL power. The D40 has to use WEP to match the D11 and the D25 doesn't even have the WEP to do that. The one thing these planes can do is out dive the D11 with that extra weight. They're still very capable dogfighters but the extra weight can make it bit more challenging than the D11 or M.
The N I haven't flow a whole lot in dogfights but I have found it to be the hardest to use. It's really heavy! It's the slowest on MIL power but it's WEP is what makes this plane a beast! If you can keep this plane light then it can really give a lot of planes difficulties. If you can't out climb them and you can't out turn them, then you can without a doubt out dive them with all that weight, and all that weight makes for some nice zoom climbing.