So you get to choose between live rendered and stored frames? Ohnoes... decisions
Well, animation rendering engines aren't exactly a competitive field so I'd guess there's not much development happening. For example, the MNG specs have been out for 6 years and got nowhere. The GIF format should be fine (for small scale work)
if the developers bothered to follow the standard. Flash is probably the way forward as it's come from one source that produces it's own (reasonably consistent) implementations.