Thrive is good, so is the Transformer. I have both. Ice Cream Sandwich is out on the Transformer (not the Prime).
Lots of folks complaining about the wireless reception on the Prime. Check out these forums:
Asus Transformer Tablet Forum
Some folks love the Prime and have no issues. If I were to get the Prime, I would make sure I buy it at a place that had a good return policy.
Out of the two I have, the Transformer (not Prime) is my favourite. If USB drive support (without adapters) is important to you, then the Thrive is great.