I'm sure it depends on what you want to use it for...

To protect from burrowing animals, like gophers, I was told by the master gardener at my community garden to use 1/2 inch hardware cloth, and to be sure it's galvanized, or it'll rust in not time.

Be sure to shop around. I found prices in my local hardware shops were pretty expensive. I found what I needed from amazon.com for $110 cheaper than in the store...

I use 1/2" to keep rodents out. I have used 1/4" but it's harder to cut and more work for me, so I keep going back to the 1/2"

Has anyone built a cover/top for your raised bed? I mean the one's that are made of wood (1x1 wood?) that you staple chicken wire to and maybe have a hinged back so that it could be lifted up to work in the raised bed? If anyone has made this could you please put the instructions on how to build a hinged top in the square foot garden thread? THank you. Margaret