if you shoot with flash very often, like more than once a week, and want recycle time fast and fury, get NiMh batteries with high mAh like 2700. it is more economy to use rechargeable batteries for this type of usage.
if you shoot forthrightly or less, get NiMh batteries with good in retain charge, like Imedions or Eneloop. it is also economy to use rechagerable batteries for this type of usage.
if you shoot once in the blue moon, get lithium batteries, cheaper and good performance.
if you only shoot less than once a year, just get Alkaline batteries as and when you needed.
lastly, if you spent so much money on getting good rechargeable batteries, it only make sense that you spend double the amount to get a good charger, remember, even good rechargeable batteries also need to replace very often, good charger can last you for many years.