Carmack (Rage): 360 is a superior piece of hardware.

[makingmusic476]

Superior because it's easy to developer for. Carmack is used to a PC-like architecture, thus he favors the 360. He's also mentioned how much he prefers the 360's dev tools.

Some past comments of his on the matter:

PS3Vault:

The creator of classic FPS Quake John Carmack, in a recent interview with BuzzScope, said that he prefers Xbox 360 over PS3 due to “360?s symmetric CPU architecture and excellent development tools.” He admits that “the PS3 will have a bit more peak power,” but power on the Xbox 360 can be easily “exploited.”

Arstechina:

"Xbox 360 has far and away the best development tools," Carmack said. "PS3 is probably marginally more powerful, in terms of raw flops and graphic operations, but that’s not really the best way to look at things. When you look at these development cycles that stretch over years and years, being 20% easier to develop on is much more important than being 20% more powerful."

[...]

"I make little nitpicky decisions about say, well, I prefer the symmetric approach that MS has over the asymmetric Cell approach, but you can do great games on either one of them, and I make fundamental decisions based on development tools and depth of documentation, which Microsoft has been superior on."

Those willing to put some extra love into ps3 development, like Naughty Dog and Guerrilla Games, will have great results. 

And as other developers get to know the ps3's architecture over the course of the generation, it won't require an extra 20% more effort or anything of the sort to get that extra "oomph" out of the hardware.  You have to figure, developers will be working with the ps3 for at LEAST the next 4 years, and over that time they'll learn the ins and outs of the system.