I think LEDninja pretty well summed things up. Probably the two biggest factors would be the price difference, and how soon do need (or want) it?
I just got my MillerMod ARC AAA yesterday, and it is stunningly nice. Just simple, small, and amazingly bright. I got the Cree P4 with .50 low and 1.25 high, and I think that is nice setup.
The low, at .50, might be a bit to bright for reading a menu in a dark restuarant, but is perfect for reading a book, and the high is quite bright enough for most other tasks.
It is NOT a throw monster, but rather an excellent closeup light, with a softer center spot and nice, bright side spill, while being a tad on the warm side of white. I wouldn't say it is a perfect beam, but I would say it is the most useful closeup light I have, and worth every penny.
One thing to consider, Eric does recommend using NiMh AAA cells if you are planning on using the higher settings.
I hope that helps some.