i dont like like the twin with a 15". doesnt sound right in the mids, but ive never loved a 15" for guitar. not that it cant sound great in the right rig, just not mine.
a dlx will break up much earlier than a twin. depending on your gigging situation one will probably be better than the other. if you want loud full clean, then get the twin.
the ocd is brighter and not as mid heavy as the fd2, atleast in the vintage mode. both can sound good but im not in love with either.
Well I own an OCD and it's a very "british" sounding pedal if that makes any sense. It totally kicks ass and nails that sound in my head i was looking for. What do you want to know about the OCD?