I have something like 20+ pcs of Sanyo 2300 mah cells, accumulated over the past few years. recently i bought 4 pcs of GP 2500mah cells, and Varta 2300 mah cells.
it may not be a fair comparison as my sanyo cells may be getting tired, but the last pack of sanyo cells are less than 6mths old, so i think they should be in good condition still.
having said that, the GP and Varta cells hold their charge quite a bit longer. GP i've had for about a month, and the Varta ones i only just got, but i've used them in the office before.
Varta cells are not cheap, but then again the difference at the counter is only a few dollars. GP ones cost about $19 or so for a pack of 4 when i bought them. i figure i will try different brands for a while because 20+ pcs of sanyo cells makes it pretty hard to tell which ones are newer. LOL!