I find that all soldered together batteries like the MS battery packs are junk, just too many complaints about them. The amount of battery you use will vary by game too and how heavily you use the controllers. I get months out of my Rechargables, I use various kinds but I don't play all that often so it's not hours and hours each day every day. Though really any Rechargables with a decent charger that has a refresh and discharge cycle will suit you well as long as the batteries aren't extremely old and have lost the majority of their capacity.
The discharge cycle seems to be crucial, the Xbox controllers seem to have memory effect, aka they remember where the battery dies so if you are just topping off the battery it won't last as long as if you discharge it in your charger then charge it back up again, this way you know you are getting a fresh, full charge. Especially if you change the batteries when the lights on the controller flash, although the controller does do a fairly good job of draining the batteries all the way even when you change the batteries when the lights start flashing, when I discharge I find about 100-200 mah left in the cells before they start charging.