I tried the "spot weld" drills, but wound up using regular drill bits, as there was less "clean up" grinding afterwards. However, i did find that 135 deg split point cobalt stubs worked the best. With he split point, the drill doesn't want to wander around (self-centering). Not ususally a problem drilling out spot welds, but more importantly, they cut with less pressure then chisel point drills. Also, the stub length allows better control. Cobalt because that's usually how split point stubs come. I used a couple of sizes depending on the size of the spot weld. 3/16" most often, followed by an occasional 1/4" .
I also used a stiff putty knife as a chisel every now and then to spring the welds loose.