I've torn down 5 cars by drilling ALL the welds. I started back when using the double sided cheapo ones you get @ H.F. (though back then I bought mine from SnapOn) and can tell you they are only as good as what you paid for them. Sure, they will work but you will go through at least 2-3 double tips on a quarter unless you have the touch of a surgeon.
I bought a set of Rotabroach (Blair brand) cuters and will never look back. The set I have has 7 cutters from 5/16 to 3/4. here is a great place and price for them
http://www.dentcrafttools.com/products.asp?id=23 there is a cheaper set
http://www.dentcrafttools.com/products.asp?id=14 but it is not capable of drilling holes deeper than 1/8" and are really meant for sheet steel. It's worth the extra $10 for the other set. I have used them to punch near precision holes in 1/2 plate. Just make sure to use a quality cutting oil.
These are the same cutters that Eastwood and others sell and you can get the spring tip or pilot tip plus extra/replacement cutters.
Also, I use a stiff 1" putty knife for seperating the panels (the kind w/the brass pommel or end cap). It gets in between without any warpage/bending of the panel and you can give it a tap on the back w/a hammer to pop the weld if not drilled all the way.
sorry for the rant, hope this helps.
Todd