I personally prefer AD&D. Specifically 2e core with 1e rules grandfathered in...or if you wish...1e with a few 2e additions...either way you count them.
It's easier to go with the flow, the classes are more defined...and characters are trained and experienced warriors (well as fine a warrior as a 0-class warrior who has a THAC0 of 20 and a d8 HD in 2e...so they took some time to be trained in the profession rather than...poof...I decide to be this class overnight...and then this one as well...etc). The archtypes are strongest in AD&D. I wouldn't play AD&D with all the kits and stuff that came into being with 2e however.
For you, that may not be the best fit however. You said you played some 3.5 so that's probably going to be what your memories of D&D are...and something along those lines would probably be the best fit.
I'd say Pathfinder is a great thing to play. This has already been posted...however...
Pathfinder_OGC
Is split into the specific areas which you need to know the rules...so want a Barbarian, simply go to the Barbarian section. Easier then flipping pages even.
If you want the entire rules as a download, or the free ones go to their download section
Downloads - Pathfinder_OGC
but seriously, it's easier just to access the page. It's free too. You can buy the books...I think the Core Rulebook can be gotten for $25 used...or cheaper on ebay if you are lucky...just depends. Not as expensive as 3.5...but I'll grant that's it's not as cheap as free.
I'd say Pathfinder would seem to be the best fit for you though...it has some elements of 4e in there too...so it may be easier for your 4e friends to swallow.
Unless they REALLY like class as an archtype with tougher Multiclassing rules like 4e...or as the same thing would be called in AD&D...Dual Classing...in which case you still might consider AD&D. AD&D also has Hybrid type rules (it's term for Multiclassing) though that's a little more strict then even 4e. AD&D also doesn't have all the neat little powers that 4e has...Pathfinder and 3e at least have feats (different then 4e feats in that their feats are MUCH more powerful, and in many instances closer to powers...such as Power Attack and Cleave and such) that will give them the semblance of dailies and encounter powers.
ADDED: So overall, I think Pathfinder probably is the easiest way...and best off you can try it before you buy it with the pages I listed above...for free!