Done (trying to be chronologic here): salvia, hawaiian baby woodrose, LSD, MDMA, DXM, 5-MeO-MIPT, 6-APDB, nitrous, mushrooms, 25C-NBOMe, 25I-NBOMe, 2C-D, 4-HO-MET, 6-APB, 4-AcO-DMT, 3-MeO-PCP, "LSBD" aka "LSZ" (phenetylamine blotters), 2C-B, 25I-NBOH, probably some others I forget
Most recreational: I would say phenetylamines in general have the most potential here. My favorite for recreation would be empathogens like ecstasy and the benzofurans, and from the tryptamine family the very empathogenic moxy. About benzofurans, note that from my experience they tend to be picky about getting the job done, ie. they will work for some and not for others. For me the two times I've done them were just as awesome as a MDMA roll. Also, to represent dissociatives, I'd say baloons are a very recreational substance. Nothing like laying down with one in the middle of a psytrance party and completely imploding with dissociation for a sec.

Great when done on serotoninergics.
Most euphoric: I think the most euphoric trips of my life were the ones I had on hawaiian baby woodrose. The acid-like depth and metaphysical quality of the trip combined with a powerful feeling of intoxication (like being very stoned but ten times stronger, and retaining all clarity) pushed the boundaries of the idea of euphoria I had. Also, LSD+DXM (the latter dropped after the L peak) was a very euphoric combination, it had a strong rough side too though. Out of phenetylamines, 2C-D was the most euphoric for me.
Most social: One of my last discoveries, 3-MeO-PCP turned out superb in terms of social augmentation. It gives an extremely pleasant dissociative/stimulating high that just goes well with group chill out and chit chat. Also all empathogens are of course very social psychedelics.