I would say that EWR is the most laid back base in the system. I bid EWR because of the commute with the intention of going to IAH when I had a little more seniority. But I like the people here and have no plans to switch bases.
I think Cleveland is one of those love it or hate it places. The people there are either very senior or very junior and trying to get out. As others have said, it is the smallest base with little growth.
On the flip side, IAH is our biggest hub, and therefore isn't as intimate as the other two. It's also to close to the mother ship, if you know what I mean.
As far as getting your base assigments, past trends show that those in the first class of each month got their picks while those in the middle or end got placed where needed. At least that was the case when I went through in the spring/summer. It may have changed now. Our new contract has language in it that prevents a new-hire from going to a base before someone already on line has requested that base. Regardless, if you don't get your first choice, you should get it after a few months.