AOL's client is written in JAVA I believe, and it runs VERY VERY slow, even on the HTC Touch Pro.
I have tried Agile, IM+, Beejive, Parlingo, and Slick, and I also believe Beejive is the best client.
Reasons being the interface supports touch navigation, its VERY fast, the interface is intuitive, modern, it looks alot like iChat does on mac os X -- with the buddy icons to the right, and the list layout looking very similar.
Only downside is that the features like direct connect with picture send and file send are not yet supported.
If you absolutely need those features, then go with slick, but the program and interface itself has not been updated in a long time -- looks like a windows CE 2003 application basically.
Agile is horrible, not only do they charge for it (even if you get a cracked version), but it also has not been updated in AGES.
IM+ is alright, but I do not like the interface. It also has been known to crash every now and then for no apparent reason.
Even though they seem to have updated it to look "modern" and be compatible with 6.1, it still looks nothing like the iPhone versions iface -- of course.
0_~ <- surge stylee