They are all good, Sigma through M&P
I know own a Glock 17 circa 1986, a Ruger SR-9, Browning Hi-Power, Sigma 9MM and a Sigma 40 SW, A SD9, Kel-Tec PF9, Springfield XD 9 and XD 40, .....I actually gave away a NIB 92FS to a friend....not sure why I did that....no matter.....bottom line? I own or have owned almost all desirable 9's that 70 percent of the market has owned.
My assessment. It really, really does matter to YOU what YOU like. Oddly enough, I thought the Sigma's were going to be in a pretty lower class of gun. Well, guess what. The aren't. They are just fine. I bought both of them for the whopping price of $279 each with rebates over the last few years. And yes, the trigger is a bit stiff but, you can either mod it or simply get used to it. I actually like the newer .40 better than the 9mm I bought a few years back...both are VE models. Both shoot anything I throw through them and are easy to clean and function beautifully even if the trigger gives me a workout.
Are they target pistols? Nope. They are good enough defense pistols though and they handle the recoil well of almost any load.
The SD is an improvement. The trigger, sight, weight, finish and overall feel is better. It feels and is slightly slimmer and more ergonomic (just when I thought Ruger had licked everyone with theirs).....I don't have particularly large hands so this SD and Ruger SR9 fit quite well. The Springfields are as good as a Glock, period. Glock is excellent to and there is nothing you can say about their reliability to change that.
In the end, I chose the SD because of the improved finish, slimmer profile and improved carry. Capacity is equal to the Sigma's but the improved finish, sight (front anyway), trigger and ergonomics was worth the extra $70 I paid. Bought it for $349 new. Not bad.
If you want a nice, slim and dependable 9mm that won't break the bank, look at this one. I don't believe you will be dissappointed. The M&P has some improvements but a bit bulkier than I like.
And for those that think the Sigma is worthless, consider this. Recently they were being sold, new, for $249 with rebate not all that long ago. The magazines are excellent and the gun feeds well. They just aren't the most pretty out there. If you want a solid, no BS pistol for a good price, these are it. I actually like my .40 more...shoots a bit more accurately for me...not sure why, just does.....
In the end, if you are considering either pistol, you will NOT be dissappointed.....and if you have the extra money, the M&P is a good option for the money. Smith and Wesson are offering a good value with out putting you in the Sig, Colt, and Kimber cost range....you don't really need to spend that much to get a good gun. These are fine and I stake my life on the SD, Sigma's and Ruger regularly. No worries. No shiite.....
The rest is noise and I have yet to see a volunteer that will step in front of either. Christ, for about $500 you can own both a 9 and a 40 Sigma or, for about $700 you can own an SD9 and a SD40.....you can't beat that.
I just wish S&W would/could lower their price on some of their mainstay revolvers in the .357 range. I love the 686 plus but, just can't seem to come up with that type of investment...beautiful revolver but, too much for me.....
Get a Sigma and an SD, you won't be sorry......