I bought the small one for 2-3 and I could fit a small dining room table and 2 chairs easily.  I did buy a small fan because it can get stuffy in there in high temperatures.  It keeps the mosquitoes out and allows me to sit and work outside.  It was incredibly easy to set up; it basically set itself up--almost comically, it jumps out of the carrying case and unfolds itself in a matter of seconds, so beware!  I didn't weigh it down with the sand bags and have had no problems with it blowing away, but I see that a few had that issue.  Very pleased with it; high quality and easy to put up and take down; fits very nicely into the carrying case.  My son is hankering after it because it's so portable and perfect, even though he mocked me when I initially ordered it ("what do you need that for"?).