My first LSD experience (which was also my first real drug experience) was alone, as were the next 3. I wasn't totally alone - the first 2 times were in a high school dorm, so I could always walk out of my room and go find someone to bug if I wanted to; but I spent the majority of the time in my room listening to music, tasting things, smelling things, feeling textures, etc. These were most excellent trips.
Then a little later, I would always trip in small groups. This would be with 1-6 others, but most frequently 2 other good friends. I enjoyed these experiences as well, expecially with the 2 good friends that were always trying new substances with me. The three of us all have/had pretty open minds, and are pretty good at not freaking out when something minor happens.
Thats my biggest problem with a group. The experience levels of all the participants has varied a lot in my trials. This is ok, but sometimes people can't dose themselves for shit, or dose at the level others are at even if its too much, etc. Then they rocket up and panic. It frequently falls on me to be the one trying to calm them down.
FUCK I HATE IT. I don't mind helping people having a rough time normally - I'll go way out of my way (to the detriment of my own experience if needed), to calm them down and smooth things out - but I cannot stand it when its something that could have been avoided if they had just listened to me. I really don't like having to hold someone's hand and tell them everything will be ok while they figet like a tweeker and fight back tears, while I'm frying nuts or coming up fast. The come-up on many psychs is bumpy for me. I often prefer to be able to sit/lay down alone for 20 min or so until things even out and I slide into the trip. I'm an anxious person, and I don't need people adding to that.
If it comes down to it, I'll always try to help though. I've been at a party (30 people or so) where a someone brought my ex-gf (who had essentially betrayed/hurt me in every way possible, over and over again). They were both dosing. Knowing them both very pretty well, I advised them to wait till some other time or at the very least take a low dose (neither had tripped before). Of course I was ignored and they both flipped out hardcore. I mean, "ohhh... shiiiitt.." serious fucking nuclear meltdown... crying constantly, wanting to die, I'm never coming back, what have I done, I have to leave this place now (~20mi out in the middle of bumfuck nowhereville) sort of thing. So I end up talking them both through it, and it ripped me up pretty bad inside.
I'm less and less willing to help those that directly ignore sane advice these days, though I try really hard to not get into that situation to begin with.
Anyway, what I'm getting at is that I don't like the mid sized things where there is something like 20-40 people. Someone is going to get uncomfortable or something will happen, IME. Whether or not I have anything to do with the drugs or people, I feel a certain repsonsibility to fix things if they do not go well, being more experienced with/clued in to these drugs than the average joe. It weighs on me, and detracts from the experience.
But when I'm with a handful of people that I know and love, people I'd take a bullet for, its great. These people are also pretty experience with these types of drugs, and the behaviour of people on them. If it gets a bit strong or if I go off on a deep inner journey and need to wander off by myself to lay down with my eyes closed, I don't want someone coming in and poking me every 5 minutes to make sure I'm ok. A periodic non-invasive check is cool - even appreciated - but if things are rough the last thing I want is someone to stare at me like I'm dying and frantically ask if I'm going to be ok. These people know and understand this.
I like to be able to do what I want to do without wierding people out, too. If I'm frying out and want to play wierdass music, climb on top of the refridgerator half naked and eat popsicles, fuck it, thats what I'm going to do. I wouldn't trip around anyone that would have a problem with odd behavior like that. Unless I'm doing something dangerous, that is.
The exception to the dislike of bigger groups are psy parties. Its quite an experience to be at an event with, say 300 people, where you know that at the least half of them are tripping. Its like being on another planet. Everyone goes with the flow, acts totally fucked up and thats normal. You can always retreat to your tent if you need to get away. Its a great combination of experiening the beauty of nature, companionship of likeminded people, the drugs, and music.