Harrah's doesn't really have any bad rooms, but some are better than others.
If I had to choose one, I'd pick the Bayview Tower, but the Waterfront Tower rooms are pretty nice. I'll try to highlight the differences between the two towers that most people favor.
WATERFRONT TOWER
PROS = comfortable, recently newest rooms, flat screen TVs
CONS = no bath (just shower), proximity to Pool nightclub (and this may be a good thing for some, but it can be noisy on weekends when people are stumbling back to their rooms)
BAYVIEW TOWER
PROS = large bathtub
CONS = no flat screen TV
I'll leave one last caveat. Both the Harbor and Bayview Tower are a little ways from the casino. Some people like that, but if you want a room closer to the casino, then you'll want to be in one of the other towers. Also, if being in a quieter place, away from the nightclub crowd is important to you, then you'll also want to avoid the Waterfront or Bayview Towers. If you can get into an Atrium Suite, then that is a reasonably comfortable room, with a separate sitting area. Those rooms aren't bad, either.
I have pictures of most standard room types at Harrah's posted here:
http://achotelrooms.blogspot.com/2009/10/atlantic-city-hotel-room-photos.html