D-11 and D-25 are a LITTLE more stable laterally because the razorback gives it extra "bite" into the air going forward, so to speak.
D-11 is lightest (least amount of gas tankage, I believe??) so while it has the weakest engine it also makes up for that by having less wieght to pull with that engine.
D40 of course has wonderful bubble canopy. Better ordinance options. And its the fastest version with the most powerful engine. It's also the heaviest, if I recall. The WEP really helps when needed (the WEP has more kick than the D11, in my opinion). From what I've heard, the D-25 is really the worst of the lot. Either take the 11 or the 40, is the sentiment I always hear. I don't fly them myself enough to know for sure, but I'll just pass along what I've heard.