Balls Up isn't showing up on the mobile App Store for me, but based on the thread for the game it looks like an ordinary keepy-uppy game with online leaderboards. I'd definitely have to go with Springball in this case. It's a lot of fun. I'm about to do a review for it actually; I was surprised by the degree to which PebbleBug has taken the keepy-uppy theme. There are different game modes (high line, hoops, and pro games) each with special bonuses and powerups, multiball, unlockables, multiple ball types, level goals, and other nice surprises. The controls are nice and responsive, collision detection is spot on, and the physics work well. It's definitely worth snagging for its introductory price of a buck.