7018 is hard to start I like 7014 it is easy to start and has good specs and a nice weld

 

6011 for pretty much anything, clean or dirty. The 7018s are very good for thicker metal, just make sure you clean it and once you start your bead keep goin til you're done. When you restart a rod, try striking it at a 45* angle, it's worked for me. All depends on how thick and what metal you're working with. Mild steel you can weld pretty much all thickness with a 6011 then go over with 7018 to clean it up. Stainless and aluminum are completely different monsters but when you get the hang of it, it's pretty kool what you can do. Very important, like most have said, don't ever look into the arc. It will mess you up pretty bad, especially the heavier rods. Good luck man and happy welding.