Yeah Trade Satoshi is very incompetent at the moment for some reason. They'll eventually get the 404 wallet running. In the mean time yes, Crex, btcpop, or nuex exchanges will work well.
The actual reason why the wallet is in maintenance doesn't look like it's related to problems with Tradesatoshi but more with the Blockchain itself and the wallet.
Tradesatoshi maintenance reason: Blockchain sync stuck infinite1/24/19