To make a real-world example, lets assume I want to build an animated sprite for an explosion. The duration of the animation should last ~1 second, and we'll say exactly one second to make the math a bit more simple. And lets assume I'm using XNA and my goal is to target both XBox (60fps), PC (60fps), and Windows Phone 7 (30fps).
My question is this, how should I build the sprite animations so that my programming is as simple as possible without simply using a timer to calculate which frame I should be on (which I feel would make the animation "choppy")?