Most of the users and Developers that I chat with over at forum.xda-developers.com agree that the GingerBread version of Android handles memory WAY better than Froyo (2.2).
Although, one of the main reasons that I run a custom/developer version of Android for my EVO4G is that they remove all the bloatware Sprint apps that come preinstalled and have a habit of just sitting in cached memory waiting to be used :-/
If I ran a stock version provided by Sprint I'd be tempted to run some sort of task killer on any of their AndroidOS's (fyi, in the dev community these are refered to as ROM's because they have to be written to Read Only Memory).
There are threads at the top (sticky's) with great info but here is what I run cause it's stable, pretty, and I get ALL DAY out of my battery!:
[ROM] - [MikRoms]- [8/9/2011]- MikG v2.45- Re-EngineeredGBSense2.1+ 3.0
I was told by Sprint that I need to have Advanced Task Killer (or one of the many task killers) installed on my phone to keep as much free memory available as possible. I have read conflicting stores on if this is truly necessary. Do I need a task killer?