Tube size

I'm looking to get some square tube for my frame. What size do most of you use? I'm guessing a 2"x3"?? What about the thickness?? First time buying this stuff, so I don't want to sound any stupider than I do right now. Thanks for any advice......

2x3x.25

I used 2x3 .188 wall.

Thanks guys, exactly what I was looking for. I appreciate it!!