The 26 and 27 are the same gun just different calibers. The subcompact 26/27 with unmodified mags leaves your pinky finger handing below the mag, but it doesn't bother me. You can add an extension but that brings your grip length to that of the 19/23 models and the grip is the most difficult part to conceal anyway. Very good guns - all four of them.
The Compacts are about 1/2 inch longer in barrel and 1/2 inch taller in grip than the subs. I also own the 19 and it too is concealable, although I prefer the 27 for deep concealment.
Which caliber do you prefer ? 9mm or .40S&W ? If you want best concealment, choose your caliber then the 26 or 27. If this is your first gun, and you are going to carry and use it for range, I would consider the 19/23 (Compacts). Slightly bigger but still conceals well.
Either way, the subs or compacts are just great. You need to handle them to see the difference though.