Best material for a welding table?

[performance]

I would NOT use stainless.
It has a problem with attracting BB's and warping with only a little heat pressure. Sure it may look cool, but is absolutely not practical at all, unless you can get it in a thick plate, which you won't be able to find easily, and is very expensive.
I'm going to have to post s picture one of my tables. I used 3/8" plate. Plate metal is the only thing I would use, because heat will draw and warp metal. The only other way I would make one is to make one like I saw out of 1" by 4" flat bar placed side by side with a 3/4 in or so gap between the bars. One of the finest tables I have ever seen because not only did it have leveling legs for making the surface true, it was great for fixing any number of jigs between the bars and bolting them down so no welding was necessary.

I did have a round table built out of a feller buncher blade. IF I could have afforded to have the blade turned flat in a lathe, at a cost of several hundred dollars, I am sure it would have been the best table a person could have because it was about 2.5" thick. I had to cut the teeth off, and it had a raised hub in the center, but it could take pounding over and over. If you find one, it will be worth the money to buy one if you have a machine shop that could handle truing it up.

[dgarnier]

It has a problem with attracting BB's

what are BB's?

[performance]

BB's: Slang term used in the industry for molten spatter that forms little balls and rolls across the surface until it welds itself to the metal then cools.