Hi, I'll just write some opinions on each dorm, but of course the best way to figure this out is to visit each residence hall yourself, especially since everyone's preferences are different.
The bathrooms work like this: there are multiple bathroom stalls, sinks and mirrors like any other public bathroom. Usually in a somewhat separated area there are more stalls with showers and there is a curtain that pulls shut. Nothing too fancy, basically like any gym locker room (minus the lockers...). I'd suggest using shower shoes just because so many people use the showers, it's more hygienic for everyone. Obviously it's better to be able to shower in your own bathroom, but it's not that bad once you get used to it.
Calhoun: I have never once been in Calhoun to be honest, but everybody calls it "Calhood." Most people who live there say it's really gross, but on the plus side say that the dorm life there is GREAT and everyone is very social. Unfortunately, the furniture in Calhoun is bolted down so you can't move it. I'd suggest putting this fairly low on your list unless you visit and like it but I can't give too much opinion on it since I've never been inside.
Kelly: Kelly is fairly nice and it's the building that is attached to Northside dining center with the "Kelly Market" like a small grocery store, Currito (burrito place), Chik-Fil-A and Subway. The bathrooms here are huge but the rooms are pretty small. The kitchens here are fairly nice I believe. The lounges are two stories with spiral staircases, this connects the guy and girl floors but because of overcrowding in the housing this year, the lounges were converted to four person rooms and so are unavailable for "lounge" use. Not sure if it will be that way next year.
Myers - Myers is where I live and in my opinion, the best dorm. It was my top choice and after moving in I knew I'd made the right decision. What I love about Myers is that it's only 3 stories (I don't like elevators too much and I didn't want to live on a very high floor). There is a courtyard in the middle of the building that is nice to do hw in (when the weather is right) and people often make food and smores on the grills out there. The floors are co-ed which I LOVE because it gives you a chance to make friends with guys AND girls outside of your major (downside is members of the opposite sex see you walking down the hall to the bathroom fresh out of the shower or having just woken up.... haha). Myers has a great social life, everyone hangs out together. 2 lounges on each floor were converted to four person rooms but there are 4 lounges still open on each floor (two HUGE lounges on the first floor. Pool table, TV, foosball, ping pong, etc. dispersed throughout the lounges). I got a great position because I am directly in between two bathrooms, lounges, and kitchens... all about a 10 second walk away from my room and next door to the laundry room (great for not having to drag laundry around but sucks when people decide to wash their clothes at 3 AM). Sorry that my description of Myers is so much longer, but it's where I live so it's easier haha.
Towers - Before I got here everyone said Towers was the BEST dorm to live in, but personally, I don't like it at all. Because of overhousing, every one in this dorm was tripled (Towers has the biggest rooms, but still are only a TINY bit bigger than Myers) but people got moved around and I think they might all be doubles now (not sure how it will work next year). I thought the kitchen/common area was disgusting, dark and unclean. I did not like Towers at all but people who live there tend to think it's okay.
To me, still, Myers is the best but it's all about personal preference. I love Myers because it's co-ed floors (the only freshman dorm that does this I believe), I like that it's only three stories, love the courtyard (except walking through it in the winter), and love the social life. Hope this helped.