FWIW...
I can't speak from as deeply-rooted chemical knowledge as some of you guys, but I definitely can speak from experience...
Of all of the research chemical "families" out there, the 2C-x's certainly seem to be the safest-feeling/least-negative-effects of the RC-categorized drugs. The DOx, on the other hand, seem to have the longest-lasting side-effects and also be dangerous in that they are so often passed off as LSD that someone could easily cross the line from high-dose to dead-dose.
My first experience with a 2C-x was with 2C-E, and not knowing proper dosing (this was years ago and I was an idiot), I went ahead and took around 75-90mg. It was pure, obtained from a chemist who made it personally, and I have never tripped harder in my life. The worst side effects were a tight-feeling-chest and brain-zaps the next day, as well as a dissociative state (at times during the trip) that I've never noticed on lower doses.
With DOB, DOM, or DO-whatever, I ALWAYS have bad experiences. Usually this can be in part attributed to my being told I'm getting LSD-25 and I end up paying way too much for some BS RC, but regardless... These RC's last MUCH longer (as long as 34hrs for me on 5 hits of DOB, unknown precise dosage), feel much more "taxing" on the body, and leave me wicked-depressed for up to two weeks following usage.
That's just my $0.02, as I don't want to get into the PMA/2C-T-7/etc discussion; too many acronyms.