It depends where I am.
At lunchtimes in the city I sit cross-legged (or "good sitting" as they call it at my son's kinder!) on this thin grey mat which is up on a meditation bench. That's pretty good.
Yesterday, and often when on retreat I sit in a chair. Strangely, I think I seem to actually get the best results in a chair despite the fact that the chair is often made out to be a position of last resort.
Sometimes I'll sit on a couple of cushions on the couch, with a cushion under each knee. That's pretty good too.
If I must sit on the floor, eventually I'll need a back rest (preferably a wall) or I'll start getting back-trouble and sciatica, and in a retreat environment it will become a distraction.
So there you go... a real mixed bag.
No lotus positions or anything... I've never even been able to touch my toes, let alone be a contortionist!