Looks like I'm in the minority, but my favorite is the one that's ready to go at all times. The one I trust most. M&P9c. Trijicons, CT. More than 5,000 rounds through it without a hiccup.
I have a 3913 TSW , that I am very fond of, easy to conceal, and I keep it loaded with Federal 115 gr. +P+ (BPLE) if I remember the designator correctly
I'm going to have to shift the focus a bit. While I like my three S&W 9mm semi-auto pistols (two CS9s and my Lady Smith!), I have become quite taken by my 547. It carries easily and just feels great in my hand. Accuracy isn't bad either!
My favorite S&W 9mm's in the order I purchased from the 80's to present.
My first S&W 9mm was a S&W 469 when they were 1st introduced and
a few month's later a S&W 559.
Then I added a 3913 and 3906 when Old Sac Armory was closing out.
Later added another 2nd 469 and then a 3914.
39-2 for fun, 3914 or 3953 for carry (and a have an eclectic collection of other 9mms ranging from Star BKS through a number of CZs and Walthers to an M59). Dave_n
Guess I`m oldfashioned too. Have only owned 4 , a NIB 39, a gently used nickel 39, a 439, and finally a 459. Have sold or traded them all- favorite would be the NIB 39.
I have three at the moment. My oldest is a 586-1 from 1984. I also have a 637 for CCW and a 908S for the same. If I had to pick a favorite, it would be the 586. It has at least 10K rounds through it and still going strong.