What exactly is better? People don't seem to know the difference between better and preference or used to.
Bearing in mind that multi-GPU solutions from ATi and nVidia took off around 5 years ago, they've both had plenty of time to make them work, and work they do.
The amount of games that dual GPU configs don't work well in are either so old that they run fast enough anyway or they're broken.
I think it's safe to say that all games released in the last 2-3 years have some sort of multi-GPU profile.
Multi GPUs have taken off big, they currently work better than ever before and offer a real increase in performance.
A lot of games you can get about an 80% increase in performance over a single card/gpu and increasingly common, games that will give 100% performance over a single card.
I notice that people who have issues with multiGPU setups are still clinging on to the issues there used to be when the current iterations were brought about 4-5 years ago.