What's the best format for transparency?

[Stilgarius]

Hello!

I have been using Premiere Pro for a while and I was using a lot of Quicktime JPEG 2000 for transparency files - Mostly because of lower file size than enormous QT with 10GB 30s clip and 250k bitrate...

As I see Premiere Pro dropped that codec so I have question - What's the best format to make a "low size" clips with transparency on it right now?

[Ann Bens]

Cineform or QT-animation but they are not small files.