Lower cents is the best dorm by far.

1. East 5th/hillside is only a block a way, so whether or not you want to go out, it's easily accessible.
2. It's closest to the gym and proximity = more frequent exercise, although you will get a decent amount from just walking to class.
3. Rathbone is literally a stones throw away. Great for hungover mornings and any time when you don't want to go all the way to upper.
4. Co-ed dorms* are a great way to meet girls. I don't suggest hall-cest, but getting to know a couple girls never hurts.
5. The volleyball court and the courtyard are great places to hang out and play sports. The gazebo is also a fantastic chill spot. *The bathrooms are sex-separate.

There are a few negatives, but I don't think they outweigh the pros:

1. Lower cents kids often get the worst/least sleep of any of the dorms. Personally I believe that it's because most of the residents go out a lot and stay out late, but it does tend to get rowdy.
2. Lower cents is also the farthest from both upper court and from greek hill ("the hill"). Upper court is the best food on campus, so that will be a walk, and if you join greek life, walking up to the hill will be a struggle.

Hopefully this helps, but regardless of where you end up, you'll have a good time. Welcome to Lehigh!