There is a tradeoff between cost and performance.
The best-performing batteries are the disposable lithium batteries, e.g. the Energizer Lithium line. These have a higher capacity than regular AA batteries and, important for photography, better sustained performance as they wear down. Also, they're noticeably lighter, which is a nice perk for something you're going to be carrying. I also like to use disposable batteries when I'm traveling, since I'd rather spend a couple extra bucks on batteries than lug a charger. Also, if your rechargeable batteries die mid-day, are you just going to carry them around in your pocket?
Rechargeable batteries are obviously a better value in the long run, particularly if you get one of the newer brands like Eneloop that claim to have 1500 charge cycle lifetime. The Eneloop (and some other NiMH battieres) also have the benefit of being low-discharge, which means they still retain most of their capacity over time. Some rechargeable batteries are quite poor performers in this regard -- you can't just let the batteries sit in a drawer for a month and expect them to still be charged when you take them out.
The Stobist actually claims that NiHM rechargeable batteries have faster recharge time for strobes than alkaline AA, despite having a slightly lower voltage, although I haven't compared myself.
If you're going to get rechargeable, I definitely recommend the Eneloops. I had an old set of generic rechargeable, and I was constantly having to charge them because they had self-discharged. (Side note: I'm told that those 15-minute rapid chargers are not good for batteries, since they cause them to get very hot. The charger that comes with the Eneloops takes several hours.)
