What type of charger should I purchase?

An automatic charger offers the greatest convenience. Just plug the battery into the charger and the charger does the rest.  

Manual chargers, although equally effective at charging batteries, require a greater level of attention. Generally speaking, automatic chargers are priced higher than manual chargers.

The formula for calculating the size of the charger required is:
The battery Ah / (hours to charge/2) - i.e. a 100Ah battery with 8 hours to charge is 100/4 = 25A charger.

REMINDER:

When the charger light goes GREEN, it doesn't mean the charger is finished, it's just that the charger has completed the boost charge which takes the battery to around 90% capacity.