Just to sort of summarize: There are basically three types of rechargeable AAs available today (ignoring the older NiCad because of its lack of any real advantage):
- low self-discharge NiMH, like Eneloops, Rayovac Hybrids, Rayovac 4.0, etc. Advantage: slow discharge when not in use.
- regular discharge NiMH, losing 1% charge per day. Advantage: comes in higher mAh ratings.
- rechargeable alkaline. Advantage: 1.5V instead of 1.2V.
Rule of thumb:
- Use Eneloops et al. if you often don't use your reader for days.
- Use higher mAh rated regular NiMHs in a device requiring more juice, like a digital camera. Also use them in a reader that you use daily, though I don't know at what level of use the plot of the higher mAh/higher self discharge battery crosses that of the lower mAh/lower self discharge battery.
- Use rechargeable alkaline only if your device requires 1.5V, and won't work on anything lower, and you prefer rechargeables. Rechargeable alkalines are also slow self discharge, which made them attractive before low self-discharge NiMHs were invented. But rechargeable alkalines have several disadvantages: not popular and not sold many places anymore, require special charger, offer many less recharge cycles before they're bad (maybe as few as 12), lifetime number of cycles is lessened substantially by deep discharges, offer less mAh with each charge cycle. I suspect most people would rather just use regular non-rechargeable alkalines.