I only do mild steel (no stainless, no aluminum).
I only have 5 varieties of stick electrode, all in 1/8":
6013, 7014 - contact rod, low penetration, suitable for thinner metal
7018 - low hydrogen
6010, 6011 - high penetration, suitable for farm use and metal that
cannot be completely cleaned
Starting out, I would get 10# of 6011 and 10# of 6013. At $2-$4 per
pound these days, that's quite a bit of money to tie up in electrode
inventory. As it is, I still have most of the 50# cans purchased at $1
per pound. The 6011 is most frequently used.