MGM is one of my go to hotels in Vegas. It not as nice as new hotels like Cosmo, but it is pretty decent. I have MLife gold membership, so I get express checkin, which is awesome.
I've never tried staying at MGM signatures, I usually stick with MGM grand which is pretty awesome. If you get upgraded to one of the staywell rooms, you get free day pass access to the spa as well, which is pretty great for recovery after all the partying.
The rooms itself are decent sized. I love the bedding in the stay well rooms. The rooms are decently clean although theres not much of a view.
The pool though, is amazing. I love the lazy river and there's always great music if there's a pool party going on at Wet Republic.