This is an old post but for those who are still reading it I figured I would give my opinion.
I have a walther pps in .40 caliber and I also have an m&p compact in .40 caliber. I love the concealability of the walther pps however it took quite a bit of time to get adjusted to shooting a pistol that is so slim. The width of the pps measures in at only 1.04 inches! I own the 40 but if I had to do it again I would get a 9mm. The .40 cal. round is alot for that partciular gun and I had to send mine back to walther for some bullet feed issues. From the reviews I read on PPS talk. com and other sites, the 9mm is your best bet. Also, take into consideration the pps only hold 6, 7, or 8 rounds depending on what caliber you have.
Now the m&p compact I love for different reasons. I love the ergonomics and how well it takes the recoil of a .40 cal. round. Because it is a compact it is pretty easy to conceal. Another advantage over the pps is the 10 round magainze.
When comparing the Glock 26 and the M&P I noticed overall the glock 26 is slightly smaller and lighter then the M&P pistol however, I would still choose the M&P. Some weapons are just too small and can be awkward to grip. If you are in a situation where to need to quickly draw the weapon and shoot you don't want to be fumbling over your grip.
If it were up to me I would handle each gun at your local shop and go from there. You may decide on something not even mentioned.