I'm building a freestanding 6ft. x 8ft. deck.Should I use 2x6 or 2x8 for my joist?

 

I prefer 2X8s, but 2X6s should be fine for a 6'X8' deck.
Here is an article with deck-building tips from Reader's Digest "The Family Handyman" magazine:
http://www.familyhandyman.com/200106/fixit/main.html
lefty, or one of the other pros in here (I'm not one) can give you more tips
Good luck!
Mike

 

6' X 8' -- you are planning on a couple of 8' beams and using 6' joists? 2X6 joists will work just fine, especially if you space the beams about 4' apart and let the joists cantilever over about a foot past each beam. That is a joist span of only 4'. I see you putting this on 4 posts. Space them 5' apart. Set pier blocks in wet concrete footings that are about 6" deep and 24" in diameter. Use 4X4 posts, and 4X6 for the beams. Set a Simpson BC40 (or similar) on each pier block, and use a Simpson BC4 (or similar to tie the posts to the beams. Use Simpson H1's or HM9's to tie the joists to the beams.