I played Ao for a year or so, 205 opi fixer. The lag isnt so bad till you either get 200 and mass pvp or make a twink and mass pvp low lvl.
We have had 150+ people per side in land wars lol it gets laggy..lag was a way to win as long as the server didnt crash. Not sure if they improved it, I left right as AI came out.
Unless they really changed things..for mass pvp (most fun) fixer/agent/doc's/engineers pretty much own. One on One fixer/agent/doc/engie...hmm well they own in both

Doc's are just evil 200+. I know they fixed a few things to even out pvp..like fixers/doc's cant use the cater's now (strongest pvp rifle) its now agent only.
The free DL dosent include expansion..they are the gravy to AO, you are severly at a disadvantage without the expansion gear but it is a great way to try the game out.
If they fixed the lag issues, this would be the best game to me, the graphics are amazing, has alot of depth, the pvp is fun but think of 200+ lvls hehe it takes awhile though the lvl go faster than say EQ2 or WoW.
Not a bad game, I enjoyed my time there lag and all.