Depends on the tarp, for my cat-cut 8x10 I use 8' or 10' lines for the ridgeline pull-outs and 2'-3' lines for the corners. When I use my flat tarp I take 6 or 7 lengths of the 2'-3' lines and just connect two or more together if I need anything longer.
For guyline I've use the old MLD twisted Kevlar line (came with the tarp), the new MLD line, and GG EZC line. The GG is my favorite because its easiest to see, which leads to less tripping, and holds any knot you like. The newer MLD line is pretty good too, but I find myself always checking to make sure none of the knots have come undone as its a little slippery.