I'm looking for something that can take the place of my Kinvara 3. I love the amount of cushioning it provides, the soft ride, the low heel-to-toe-ratio, the flexible and breathable upper, and its low weight. What I hate about the shoe is the how it rubs my left pinkie toe. I did a half-marathon training run this weekend and just had to stop to readjust it. The rubbing has gradually worn down the upper to the extent that my pinkie toe is just about ready to poke out of my left shoe.
After the run I tried on the Kinvara 4 and found the upper fit and the materials used for the mesh to be very similar to the K3, thus I elected against buying them. The sales rep had me do some sprints on the Brooks Pureflow, the New Balance MR1400, and the Saucony Type A5. I didn't like the racing flats because they were stiff and didn't offer as much cushioning for my taste. The Pureflow was soft and well cushioned, but it felt a clunky and inflexible.
I've also considered based the Asics Gell Lyte33 v2 and the Skechers GoRun 2, however, I've yet to have a chance to try them on.