I'm a big fan of the droid form factor (I love my physical keyboard)..yet between those choices, I'm not sure I'd include the d2. its getting a bit old (as far as these things go) compared to two phones that aren't even released yet. (and if you want 4g, then d2 is definitely out).
I'd say the bionic might have a bit more life on it, in that it will be able to utilize android versions optimized for dual core...however, tbolt being on htc will give it some life if you are rooting. (i mean look at og droid, its still alive and well due to being so open to the dev community)
me, personally, I don't care one wit about 4g, since where I live probably won't get it til the very end of the 4g rollout. (att got 3g here a couple months ago, and tmobile still doesn't have 3g here)