I am going through the same thing as you, but am a little farther ahead it seems. I have a M&p9c and took my carry class just the other day.
I have a holster on order from Ryan Grizzle at
http://www.rgrizzleleather.com/His stuff looks awesome and he was great to work with. A bit of a wait, but many of the great holster makers have a wait.
I looked at a ton of sites and in stores to find what style I liked the best and what features I wanted. I think its such a personal choice, that you have to do what feels and looks right to you. My style of dress is pretty casual where I can probably get away with OWB most of the time since I dont tuck in my shirt much if ever, and i freeze easily so have a jacket most of the time. Personally I wanted a slide guard/sweat shield since I have a thumb safety and wanted as much comfort as I could find. Some holsters had it, others didnt, and others it was an option. I looked at what everyone made, found a style I liked then compared the styles between the the different holster makers and found the one that had the features I liked best. The hard part for me was the overwhelming number of choices that exist, it didnt make it an easy choice. These were my top contenders, there were some others like milt sparks (HUGE wait time, though I might order one some time just to see his work) and a few others that maybe didnt have exactly what I was looking for so I didnt save them:
For leather (which, personally I am a fan of) I looked at the following:
Ryan Grizzle -
http://www.rgrizzleleather.com/TT Gunleather -
http://www.ttgunleather.com/Sideguard Holsters -
http://sideguardholsters.com/ (forum member here)
UBG Holsters -
http://www.ubgholsters.comMitch Rosen -
http://www.mitchrosen.com/index.htmlMany other people have mentioned the following:
Crossbreed Holsters -
http://www.crossbreedholsters.com/Galco -
http://www.usgalco.com/default.aspDeSantis Holsters -
http://www.desantisholster.com/Safariland -
http://www.safariland.com/