Get one with independent single channel operation, meaning that you can charge one to four AA or AAA cells independently. Otherwise you'll have to charge two batteries at a time--and you'll want to charge single cells if you move into a flashlight that requires either 1 cell or three cells. You should also match actual battery capacities fairly closely in two cell lights.
I just received a LaCrosse Technology BC-900 charger and I want to make a pitch for it even though it's not my fastest one. There's also a brand new MAHA charger that does this, although I've read one review that indicates it has more limitations than the LaCrosse--and is about 50% more expensive. This has four independent charging and discharging channels and can be relatively fast--i.e. charge to full in 1 1/2 hrs. You set the charge/discharge rates. However, the beauty of it is that it gives individual readouts for each battery and lists the voltage, current, time per segment and capacity of the battery at the press of a button. It also has four modes: charge, discharge, refresh, and test. This allows you to discharge and then recharge a battery--over and over if you need to. You need to do this periodically to NiMH batteries because they become conditioned to a lower capacity than rated, sometimes severely so as time goes on. This can bring old batteries completely back to life!
It allows you to see the total charged capacity in mah of each battery, when charged fully too. This is major since otherwise you have no idea of how well your battery is performing. It's (or was a few days ago) only 39.95 and has free shipping on Amazon.
I have a faster charger with independent channel charging too, but not with digital readouts and discharge capability. This is only one of two that I'm aware of that can do all this. Great little charger. Oh yes, it is supposed to work for NiCads too.
