The thing that sells me about a ball usually, is what I see from the ball when I see it in person, in terms of how it rolls through the pins, and how much control of the breakpoint it has. Another things is obviously the area the bowler appears to have, missing outside, or inside. And of course, combining who's throwing the ball, with the reaction it's giving. If I'm not watching someone throw it, I'm probably looking for a lower RG, lower differential, unless I'm planning something out of the ordinary for me with the ball.