I've got an XDM .40 and a Colt Series 80 .45, and love them both. I've had the Colt for about 15 years, and I shoot straight as heck with it, and the thing'll feed beer cans...I can't recall ever having a jam.
The .40 is a recent purchase (on Election Day, actually)...got a nice price on it and it's fun to shoot as well. VERY manageable recoil...much more controllable with double taps than another .40 I had.
The two calibers are just different feeling, but both are good. The .45, to me, is much more of a torquey-spring kind of thing...whereas the .40 is much more of a sharp push back.
Like many earlier posters, I'll tell you just get the gun...you'll be glad you did!