For heavy oil, go with either an Alpha Crux or maybe the Sure Lock that comes out tomorrow, which I have not tried yet but reviews suggest it will be a great ball for heavy oil. For medium oil, if you want a hard hitting asymetrical ball, you can't go wrong with either a Snap Lock or a No Rules Pearl. For medium breaking down to dryer conditions, go with a Crux Pearl, if you can still find one undrilled for sale. For dry to almost no oil left, go with a Pitch Black or a Pitch Blue.