Okay, I'll 'fess up, I've used both. But I've used the Crank Brothers with a platform, not just the eggbeater.

I learned on Crank Brothers clipless -- I wanted a platform for just hopping on the bike for errands and around-town, and clipless for longer rides, and the LBS swapped the crappy stock pedals for a pair of used Mallets. You can adjust the amount of "float" before you clip out with Crank Brothers -- I started with the easier 6 degrees, and now have them on the standard 15 degrees. You set the float by which cleat is in which shoe. Unclipping is parallel to the pedal.

My 1998 Bianchi Eros had shimano mountain pedals on when I bought her. There are two different shimano cleats. One has little (no?) float, and you can only unclip parallel to the pedal. For a couple bucks more, you can get cleats that unclip in multiple directions - for a panic stop (or for a mountain bike), you can even rip them out straight up with enough pressure. This is the only cleat set that I know of where you can rip out the cleat straight up... depending on the perspective, you could view it as "training wheels" or developing "bad habits" if you want to use other clipless systems. I still have these on, since I haven't decided on what clipless pedal system I want to go with (I'd really like Speedplay, but the road and mountain pedals do not have compatible cleats).

I haven't found any difference between the two as far as pressure needed to clip in or out; it depends a lot more on how new the cleat is. It is usually a bit easier to clip in and out with a newer cleat.