Depends on your "hand" and the oil you GENERALLY see.
I generally find solids more adaptable to a variety of conditions, but lately I see only fairly light oil. If I needed one ball for now, I'd go with the RS-1. If you told me I had to bowl on an unknown condition and I had to pick one of these balls, I'd probably go with the RS-X.
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Just like hand grenades and horse shoes, in bowling you only have to get close ...
CharlesT