To me, the best bowling balls are all about useability and userfriendliness. There are times when we need the ball to dig in at our feet, and there are times when we need skid-flip, but the best ball motion in my book is the one that you can use in tournaments and league alike, and that starts with midlane control.
I love bowling balls that clear the heads but really dig in firmly in the midlane, something that gives you the confidence that you can maintain speed without having to worry about the ball squirting on you and shooting past the breakpoint. Now, sadly, sometimes that midlane dig causes the ball to expend too much energy early, leaving the backend flat, which results in poor continuation and pin carry. These balls are normally labeled "benchmark balls." They are good for reading patterns, but they tend not to be the pieces you really go to if you're looking to score. As such, they tend to only truly be appreciated by tournament players.
However, if you can get a ball to dig into the mids firmly yet still provide a smooth, rounded, continuous arc that stays true through the pin deck, I think you've got a real winner on your hands. I've found a few of these balls over the years, but they tend to be few and far between.