Here is a performance test by Jack at GreenSock who created TweenLite and TweenFilterLite that tests Tweener, TweenLite, Fuse/ZigoEngine and Twease animation kits for flash. This test is only AS2 but in this test TweenLite is quite a ways ahead in means of performance for many tweens via code. I would like to use this in AS3 to check the speeds there as well but from the onset it appears if you have many tweens that the smaller TweenLite kit compared to the AS2 version of Tweener and Twease is the better bet for performance.
Personally I don’t do much AS2 other than maintenance or converting to AS3 so I will be digging into this further this week in AS3 to check the speeds.
In Jack’s AS2 benchmark it appears they are pretty even up until around 150-200 Tweens per half second. If your application is built in AS2 and has more than 200 Tweens per second (very possible in gaming and just to have processing left over for other things) then TweenLite seems like it has less overhead. TweenLite is pulling in a respectable 10FPS on this machine at 500 tweens per .5 seconds.
UPDATE: Jack has updated the test to include AS2 (the dog) and AS3 for Tweener and TweenLite. This version in AS3 the threshold is much much higher and Tweener at 1200 tweens comes in around 10fps on this machine while TweenLite comes in at 1200 tweens at 15-20fps. They again are pretty even until around 800 tweens per second on this test machine where a critical mass is hit, at that point TweenLite starts scaling a bit better and around 1200 tweens is roughly double the FPS. I need to look further at the benchmark test as it is made by one of the authors but Jack is a respectable source and offers the source so anyone is willing to look at this. Results will vary but I think this still shows Tweener has a slightly smaller overhead (which when you compound it with many short tweens it adds up) but does not negate the use or quality of Tweener as 1200 tweens per half second is very respectable thanks to the new AVM2 virtual machine in AS3, but it is always important to perform to save up room for other kits such as Papervision3D and memory for more assets. I think this has been a very worthwhile exercise and I think that a need for a comparison tool for all animation kits in AS2 and AS3 (or just AS3 as we move forward), it will only improve both toolkits. Also, not just straight tweens but bezier, color, filters and general movement.