The Sig is kinda big, but it really does fire amazingly. The controls are comfortable. The trigger is SMOOTH. The accuracy is comparable to the all steel Sigs. I love mine and have never had a problem with it at all.
That being said, I can't comment on the SD9 because I have never fired one, just fondled.
I have a Sig Pro. It is without a doubt one of the most overruled guns out there. A lot of people will hate the "plastic" feeling of it. Well I think there's a perfect balance of steel and polymer. I also think it's pretty damn reliable and accurate. Plus they come with tritium night sights standard (well mine did anyway). It's the jack of all trades Sig. I don't know too much about the other pistols but I can tell you this about the Sig Pro. It's great. If you can find the right deal on it go for it.