Harrah's is the nicer of the two properties - it has the Pool which is a dome covered pool area that at night doubles as a club and haven for the young and obnoxious. Bally's is a sprawling property with three distinct casino areas: the Wild Wild West, the Claridge and the Park Place casinos. Bally's rooms probably also have the most hit or miss potential. (some of the rooms in the Claridge Tower leave a lot to be desired.)
Bally's is definitely right in the middle of the Boardwalk. Caesars is right next door and Trump Plaza is right next to Caesars. Caesars has the Pier shops - or if you prefer, there's the Walk on the northwestern side of Bally's.
Without a car, you're a little more remote at Harrah's. There's a walk path that winds over to the Borgata and you can walk over to the Golden Nugget as well. (not easily though.) Otherwise, you are dependent on the Total Rewards shuttle, the jitneys, or a taxi to get to the Boardwalk.
I'm with Jeanne-Marie on the casino at Harrah's. To me it always feels cramped and has low ceilings.