I've developed in Flash for a few years and have nearly always used the default frame rate -- 12 fps -- out of a desire to maintain animation speed on slower computers, and since there's plenty of classic animation out there that looks just fine that way.

However, I'm finally starting a project that will require Flash Player 9, so we're doing it entirely in AS 3.0, and there will be no backward-compatibility issues; it's a clean slate. The site will be relatively traditional — no 3D, no wild bitmap parties — but will contain various animations of both vectors and bitmaps. Of course I plan to use bitmap caching wherever practical.

So my question is: what framerate should I use?

The arguments IN FAVOUR of a higher framerate are:
— smoother animation
— since I'll be using an AS3/FP9 combination, I can rely on the 30x speed improvement of the player over past versions, and even 'slow' computers can handle my relatively simple animations (this is 2008, after all)

The arguments AGAINST are:
— older computers aren't as fast as I'd like to think, and there are enough regular folk out there who won't see a 30 fps rate even WITH FP9
— Adobe still (as of CS3, anyway) has the default rate set at 12, so presumably they feel the lowest common denominator still can't reliably handle more than that
— since decent animation can still be had @ 12fps, and since it's hard to get reliable information on what to really expect from a broad base of users, stick with what you know works

All things being equal, it's pretty obvious that 20, 24 or 30 fps looks smoother than 12, so I'd like to use it ... all things being equal.

Any thoughts/arguments most appreciated.