I have a couple of ferrule crimpers and the self-adjusting ones that
@buzzlightyear linked to are by far the easiest to use, so get them as your starting point. They will do 99% of jobs perfectly.
Having to get the ferrule in to the right gap in the sized sort is more effort and if it get stuck in the wrong one (or the "inverse gap" between sizes) is a bit of a pain!
However, those cheap self-adjusting ones don't crimp sizes from 0.5mm or below well, not really a problem for power wiring though. For that I still use some simple manual crimpers like these:
Discover Maun's Bootlace Crimping Plier, for crimping insulated bootlace ferrules in sizes 0.5 mm2 to 16 mm2. Buy your Bootlace Ferrule Crimping Plier online today.
www.maunindustries.com
I also have an expensive RS set for 10-35mm that is handy for tri-rated or dual 6mm ferrules, etc. They do a very good job but are hard to justify for most folk's jobs:
uk.rs-online.com