Here at Noam Design our flash developers typically use Actionscript animation over timeline tweens. The advantage to that is significantly smaller file sizes and smoother, more stable movements. For most developers, it is much easier to deal with your motion in terms of time rather than in frame. Also, when a client requests a change, editing a small snippet of code is far quicker than attempting to adjust the objects on your timeline (especially when you’re dealing with many objects on the stage). In addition to the built-in Tween class, we have recently started using these two particular open-source Tween engines which we think are the best out there:
Tweener (http://code.google.com/p/tweener): This engine has a very easy simple syntax to it so it’is good if you are just getting into using Actionscript for your animations. Also, it is a rather small class, adding only 10.4 kb to your SWF.
TweenMax ): This one has a lot more versatility than Tweener does but takes a little longer to get the hang of. It is slightly heavier at 11 kb, but offers a wide range of options to
customize your work.
More to come,