Used: LSD, LSAs, Mushrooms, Mescaline, 2C-I, Nitrous, DXM, Salvia, amanita muscaria, diphenhydramine, probably MDA and other MDMA-like substances in street rolls but I can't be sure
The most easily recreational above is nitrous, simply because it is a short time commitment with little risk of a negative experience. However, it's hardly social to be zonked out on dissociatives and, while nitrous can certainly seem somewhat euphoric, it's also numbing which makes the euphoria unusual and hard to compare to non-dissociative euphoria. Of the longer lasting substances, I'd say the most recreational is 2C-I; it has never approached ego death, extreme negative thought loops or terror, etc. even on fairly high doses, at least in my experience. LSD is usually a blast, but it can get much more intense and I imagine most people here who have more than a couple LSD trips under their belts have had trips that they would not call recreational in a traditional sense. If recreational is understood to mean 'the fun aspects of psychedelia (body high, visuals, altered thought process, sense of novelty and wonder at common activities and events, etc.) with minimal potential for a bad or difficult trip' then 2C-I would have to be the one.
2C-I and LSD vie off for the euphoria crown. Every serotonergic psychedelic I've used has a pretty high potential for euphoria, but psilocin and mescaline can be quite rough physically at times as well. LSD has the twin honors of having spurred my most intensely euphoric trips to date and having virtually zero risk of any unpleasant body load. 2C-I is more consistent in degree of euphoria; while it's never passed the intensity of my best LSD trips, 2C-I's euphoria is consistently above LSD's average. While I sometimes get minor body load from 2C-I, it's never been severe enough that I felt worse overall than I would sober for more than a brief window on some of my first couple come ups. Overall I think the euphoria crown goes to 2C-I, although if I had both available in quantity side by side to compare I might change my mind - my 2C-I use started recently, whereas it's been about a year and a half since I tripped on acid.
As for most social... Despite its recreational 'softness' and stimulant properties, I'm not sure I'd feel particularly comfortable in public on any significant dose of 2C-I. My 2C-I trips have all been solo thus far, which my be shaping my opinion here, but the combination of physical intensity and the headspace it puts me in seem best suited for some degree of passivity; even chatting with people online felt at times like an annoying obligation not to get distracted and focus on something else. If I had 2C-I available back in college, I may have a very different opinion here; set and setting are powerful forces indeed. Memories of several LSD trips back at school make me feel very comfortable socially with the material (although obviously only in appropriate settings; a small gathering with friends or even a pseudo-public party is one thing, but places with lots of disinterested adult strangers and/or authority figures may not be the best locales). While it can get quite intense mentally and visually, its lack of any body load makes me more comfortable with situations not completely in my control, such as social settings. The more body load I have, the more I want to be solo tripping so I can drop what I'm doing on a whim, curl up in blankets, dress up or down, etc. without having to think about other people and how my actions affect them or might need to be explained to them. This is probably just an idiosyncrasy of my own approach to tripping but for me at least, LSD wins out for social psychedelia. Low dose DXM is also somewhat social, although if I wanted to socialise with a feeling of mild dissociation I'd probably just drink.
