Ac/DC chargers will charge most common chemistries in use today - lipo, life, NiMh and others so that won't be the deciding factor. What you plan/need to charge will have more impact on deciding that charger features as all these are pretty full featured as well.

AC/DC chargers are limited in output power - 50watts is common, with other available with 80 and ~100watts. Price rises with charger output power as one would expect. If charging only 2S, 50watt charger will probably suffice. Personally, I'd get an 80watt in that case just to have some extra and let the charger works at a lower duty cycle.

80 watts will take care of a lot of 4S capacities before you run into charger current limiting and extended charge times. The step to 100watt charger is a large one cost wise, but needed if charging 4S packs at 1C with more than 5000mah.