I've got three IWBs--a Milt Sparks VersaMax II, a Comp-Tac MTAC, and a Galco Ultra Deep Cover. The VersaMax is sized for my Glock 26, and the other two work with the 26 or my Glock 23.
The Galco is super easy to use--slip it over your waistband, loop it under your belt, tuck in your shirt (blouse?) and you're ready to go.
The VersaMax is beautifully crafted, but when using the Kydex clips (as opposed to leather loops), a absolute bear to get on or off--the clips are so tightly tensioned that it literally takes me three or four minutes to get it on and positioned properly.
The MTAC, while not as "rich" looking as the VersaMax, is equally well made. It's perhaps a bit thinner and more comfy, and is about as easy to put on as the Galco. However, the "C" clips are somewhat more noticeable than the other two.
Overall, I like the MTAC the best. This really pains me to say, because the VersaMax is so purty (and I had to wait forever to get it after I ordered it). I may try the V-clips from Comp-Tac, just to see if I can achieve a bit more concealment, but of the three the MTAC works best for me.
The folks at Comp-Tac have just come out with a close relative of the MTAC that is supposed to work well for women:
http://www.comp-tac.com/product_info.php?products_id=114.