After an idiot sent me my first Voodoo5 5500 PCI in an envelope and it was bent up, I purchased another one.  Comparing the two, they're different cards.

With the cards fan-side up and the gold teeth facing me, both say REV A1 under the right-most fan.

However:

The first card has Toshiba RAM from Japan.  It also has three things the second card does not: one small chip Southwest of the left-most fan (appears to have the Texas Instruments logo), one larger Silicon Image chip Northwest of the left-most fan, and one small capacitor North of the Silicon Image chip.  Flipping over the card, with the inputs on the right side, it is labeled 94V-0 2900.

The second card has Samsung RAM from Korea.  It has space for but lacks the three above components.  It is differently labeled on the reverse side as 94V-0 2700.

I did a search on this forum and couldn't find anything on the different cards.  What is going on here?

The "2700" and "2900" are the dates of the PCB (27th respectively 29th week of 2000). Maybe 3dfx changed some small things but the changes weren't big enough to vindicate a new revision of the PCB.

So the 2900 is presumably better if we can equate additional changes to improvements.

Which one is more rare?

Nobody knows?  Really?