'Best' table would be a highly debatable point, but a good size is 2' x 16'. It is narrow enough to work around and easy to get from one sheet of 4x8 plywood or (my favorite) OSB.

Actually, I make 2 benches which are each 8' long. For each bench I use 7 pieces of 2x4 which are 15" long. These are sandwiched between my two straightest 8' 2x4s. 1 piece goes in the middle, and there is a piece flush at each end. The remaining 4 pieces are spaced evenly inside. That puts them 16" apart on center. These are held in place by 2 16d nails driven through the side rails into the ends of the spacers. The final frame is 18" wide and 8' long.

Legs are 30" long pieces of 2x4 bolted to the sides at each end with a 1/4" carriage bolt 3-1/2" long. I use scrap plywood or 2x4 to brace the legs. The legs can rotate on the bolts and fold up, which makes storage easier.

If you already have sawhorses you don, need thse legs. If you don't have sawhorses the legs are far simpler, cheaper and faster.

The 24" top overhangs this frame by 3" on the two long sides. I find it is easier to clamp to the tabletop with this overhang.

two carriage bolts hold the tables together.

You need a pound of 16d nails, 10 carriage bolts 3-1/2" or 4" long and the same number of flat washers and nuts. I find 1/4" bolts are fine, but you can certainly use 5/16" or 3/8" if you want to.
I use 1-3/8" drywall screws to hold a 1/2" OSB panel to these frames. Usually I use just 4 screws. I want to be able to remove the tops, or flip them over when worn--and I don't want to have a lot of screws in my way if I do any cutting. The fewer obstacles the better.

At a minimum you need 8 2x4s which are 8' long. Buying 10 is a good idea. Select the straightest 4 for sides. Cut 2 legs 30" long from each of the next 4 2x4s. Cut the 15" spacers from what remains.

Some lumber yards will rip your plywood or OSB for free, or for a minimal fee. It makes the pieces easier to handle and get home. If you can get them to cut the spacers and legs for you , too, you'll be ready to build as soon as you get home.

Hope this helps.

PGJ