At this exact moment, I would have to say the Behold 2.... however, just by a tiny bit. And that's assuming you don't want a physical keyboard. Even then, you're going to have to make some changes to get rid of Samsung's terrible "TouchWiz" interface.
But there is really very little difference between the MyTouch and the Behold 2. They both have the same super crappy 528mhz qualcomm processor, which is what causes the G1, MyTouch, Hero, Eris, and Behold 2 to stutter and be generally rather laggy.
I would definitely agree with the others.... there will be sooooo much difference between the Nexus One and the MyTouch it will totally put the Behold 2 and the MyTouch to shame.
Besides, the Behold 2 is just crazy over priced. I mean, it's $30 more than the Droid, and $130 more than the Eris... both of which are much superior to the Behold 2. (other than the fact that you'll be paying way more for Verizon.)
So yeah, wait a month or two. You'll be glad you did.