If I had space in the box for the breakers, I'd go for multiple 15 amp circuits with a small number of outlets on each one. If I didn't have space for the breakers, I'd go for 20 amp circuits, and more outlets on each circuit.
I'd prefer the 15 amp thing for a couple of reasons:
Fewer games per circuit means that anything going wrong on one circuit isn't going to affect as many games at one go. I'm thinking things like a game shorting and tripping the breaker, but this also applies to electrical noise issues.
If I have fewer games on a circuit, I'm less likely to run close to the edge on the load limit.
15 amp outlets are the most common thing around, so in the future if someone ends up replacing an outlet without paying attention, they'll almost certainly grab a 15 amp outlet. That means that if I use 20 amp circuits, there's a small possibility they'll be setting themselves up for trouble. Now one can legitimately say 'well that's their problem', and be absolutely right. But I've been doing software (and trying to keep my co-workers out of trouble) for so long now that I inherently think in terms of 'how is the next dipstick going to screw this up, and can I make it less likely he'll kill someone?'. Proof positive that software DOES make you weird.
