I'm not going to trust Trex due to them shutting down US and the fact I think the market will become rational soon and it will go Gox when USDT goes boom.
I *think* you are confusing Bittrex and Bitfinex?
I think you are correct!

AFA Bittrex, I saw quite a few issues with withdrawals when checking them out so never rechecked. Has that been addressed or am I misremebering that as well?
Well... its purely anecdotal but I have had exactly ZERO problems with Bittrex. To be honest I am not sure why they don't have more volume. Verified accounts can withdraw 100BTC at a time.
But seriously YMMV... I have done very little volume with them.
When I was about to sign up there, I read the user agreement. NEVER do that lol! Scared me away.