I've done all three in multiple settings. On the floor has the fattest sound, but it's probably coupling effect. The downsides are that it's blasting the backs of your knees and kind of hard to hear without decapitating the audience. In a recording situation a mic wouldn't hear all of that coupling, so your recorded sound would be A LOT brighter than what you hear in the room. On its side looks goofy, but is probably the best compromise sound-wise. The biggest downside I can think of is that the head won't fit on top. These days I mostly use a 1x12 combo, but occasionally I'll pull out my 2x12; I use both on a stand. You can hear yourself well and mic'd sound is closest to what you hear in the room, but the head might want to slide off if the stand is angled.