When you say glass, I assume you mean no substrate at all? I'm really not keen on tanks with no substrate, it's rather like a room with no furniture. Gravel or sand is okay, my preference is sand as I believe it keeps your tank cleaner.
I would say to people if you want a nice tank that stays looking nice, don't bother getting oscars. Not every Oscar is a vandal, but most are. The chances are you going to have great big pits dug in the substrate, ripped up plants and rocks moved all over the place, that's just the nature of having Oscars. I actually think this is part of the fun of having Oscars.