Just the regular plain SLR. I've tried the XP and the Trans Am SLR - both have more padding and the cut-out but they don't feel like the same saddle at all.

The main thing here is to get a saddle that's relatively flat and without too much padding - you should try to get as much of your perineum and sit bones on the saddle as possible mimicking a real seat. Too much padding chafes and irritates this area so that's a no go.

You want a saddle that will get out of the way -- so you don't have to adjust yourself in the saddle.