The best I have sat in are the ones that Wayne (Ninja) Davies has had made. Loads of room for a couple of decent sized people, not the pygmies that some "double" high seats cater for. If you do a search i am sure this has come up before as John Robson (YRS) had some made as he liked Wayn'e so much.
I bought one from Grampian High Seats which is very well made, but it's never a double high seat.
Regards, Simon