Unfortunately, u are comparing like addons here. Recap is sort of the predecessor to recount(I dont believe they were trying to make a better recap or anything, but everything recount does, recap was made for, its just super old).
Both have been updated very recently, Recap is mostly non-ace2, no idea about Recount.
Recap is listed on the Ace2 listing because someone is uploading it here for the current author, who does his updates to curse.com.
I am actually going to try out Recount a bit tonight in a raid. I was using Recap for a long time, and depending on ur settings, it can be a huge resource hog(it can store the past 5000 events that happened in the combat log, so u can check how hard the tank was hit for, hit by hit. Or how hard ur last 20 shadowbolts hit for, etc. It also has the standard detailed breakdown that Recount does, per spell, per player, etc.
I have heard at least 1 person had a problem with recount this patch, where any time a mob dies he got about 2-3 seconds of lag. He is the only one ive heard say he had a problem tho.
You really have to be specific here. Both recap and recount give you control over the amount of data collected. If you check the timed-data flag for all possible mobs and players in recount you will hog memory (and there is a warning about that in the ingame tooltip of recount). If you uncheck some or many of the collection flags you can throttle and control the data collected.
Most people will in fact be perfectly fine to disable all timed data collection and just keep the death flag for players (and disable it for all NPCs).
Same with recap, there are a number of things to use it in hog mode or in slim mode.
So the real question would be: What feature you want and how much memory would you need to get it.