Conclusion / Summary
Recommending one of the cards is not particularly easy. The only card which doesn't run absolutely stable at their default chip clock setting is the Quantum 3D Obsidian 2 X-24, but its default is a pretty high 95 MHz. I had to clock it down to 94 MHz to have it run properly for a longer time. Considering the high performance a dual Voodoo² system provides, almost every card could be recommended. The Quantum 3D X-24 card only consumes one slot; but this is the only real advantage. The Direct3D performance and the temperature problems keep me from recommending it straight away.
Diamond proved to have a very fine Voodoo² 3D accelerator. First it is possible to overclock it to 98 MHz with some cooling (and the case left open of course), second the package contains some CDs with various games or game demos, which should keep you busy for a while.
The test showed that 8 MB cards are still more or less equivalent to the 12 MB types in regards to performance. As you have seen with the Quake II high quality benchmarks however, this could easily change with games using more 3D features like e.g. trilinear filtering, so going for a 12 MB card now is the best you can do.
Not all test boards have TV out, and it may be that you don't even need this feature. However, if you've got the chance playing your games on a large TV monitor screen, you will certainly enjoy it. Cards that are equipped with TV-out are the Canopus Pure3D 2, the Hercules Stingray 2/TV, the Miro Hiscore² and all Quantum3D cards.
2D Picture quality
The second generation of Voodoo cards is certainly much better than a standard Voodoo1 card. Some cards have proven that they can pass through a pretty good signal, even for resolutions of up to 1280x1024. These are the Diamond Monster II cards, the Quantum 3D Obsidian 2 PCI and the Miro Hiscore².
The best cards for overclocking are the Diamond Monster 3D II and the Miro Hiscore². Both are able to run at up to 98 MHz - if you accept the expenses of cooling! Otherwise you will face serious temperature problems. Canopus' Pure3D 2 is the only card that comes with a little fan, but unfortunately it was still not as highly overclockable as the above mentioned boards.
The performance gains of overclocking a Voodoo² are only around some per cent even with a Pentium II 400. Maybe it could be worth it with a 500 MHz CPU, but in this case I would rather recommend going for a Voodoo3 card, once 3Dfx decides to supply it!
In my opinion a very important factor for buying a Voodoo² board is still the price. As you've seen the performance differences are not much worth talking about. As long as the card doesn't spoil your decent picture quality you can buy almost every product. If I would have to decide between e.g. the Miro and the Canopus card, I would take the cheaper. Please also take a look at a possible TV output. It may be a reason for you to spend some extra money on a card with this feature. The same applies for bundled software.