I have a Droid Incredible and I love it, but it was nearly obsolete when I bought it last September and it's certainly well down the path of obsolescence now. Just for that reason alone I wouldn't recommend the Incredible at this point.
From what it sounds like, the whole reason why a person would buy a Samsung Fascinate was simply to avoid the obsolescence of the Incredible. To me it doesn't sound like it would be the best option now or in the future, plus it sounds like Samsung, while they normally have very good products, doesn't have the greatest reputation with their cell phones.
The iPhone is always a good choice, but as someone posted earlier, you have to ask yourself if you're that desperate to pay a premium for a phone that is pretty much known is going to be replaced by carriers in just a few months. The iPhone 4 is still obviously going to be a good phone, but my impression with Apple products is you're always left "wanting", and in this case you'd be doing it to your self with impatience alone.
The Thunderbolt is supposed to be a simply outstanding phone, and if you're wanting to go the Android route (and since you only listed 3 Android phones I'm guessing it's a serious consideration) this is probably your best route.
I guess for me it comes down to this - if you just "have" to get the Apple product and you really just can't wait for the new phone to come out in a few months, go ahead and get the iPhone - it's not like the iPhone 4 is going to become a horrible phone overnight. If you'd rather go the Android route, I'd go with the Thunderbolt.