Depends what you want. Informative? Chuggaconroy, HCBailly, most of the really "popular" ones. I've never found any of them to be overly funny, but eh.
Want to watch someone who's funny? MoogleFTW, IdleSwineProductions (the Chamber of Secrets LP is so freakin' funny), MadameWario, Mangaminx, chickenfajita12, letsparty132 and pretty much a lot of "low-key" LPers.
Dunno why some people say chuggaconroy is the best LPer, though. Not to bash the guy but he's not funny at all. The best thing that's come from him is the video where he found a shiny and freaked out.