ORIGINAL: goirish
what ever kind you buy, get the ones that ratchet. Some of the crimpers is a two step process and hard to hold the connector in and put the wire in. With the ones that ratchet you put the connector in, close crimper so it just holds the connector and then insert the wire and squeeze the crimper. One step does it all.
"ratchet" crimpers are required for real aviation. They do not allow (if used properly) under/over crimping. Still must obtain correct crimper, wire and terminal or all bets are off.