To be honest, nothing is stopping you from downloading both, flashing one of them, seeing how you like it for five minutes, flashing the other one, then comparing. You don't have to restore all your apps and change all your settings to get a feel for how a ROM looks and behaves. It will take no more than 30 minutes of your time (plus the extra time it takes to download both, of course). Once you decide which one you like, then proceed to restore everything. I think you'll find that myn's has a little more polish to it, but mikfroyo is noticeably faster. Beyond that, myn's may have a few more theming options, but most of the mods out there now are available for both.
As for LP, it's no different than stock. If you use it, you're still not going to be able to use HTc widgets. Speedwise, though, everything that makes mik's faster is more of a system-wide type of thing. You're likely to notice any speed improvements with launcherpro, specifically, but it certainly won't be worse.