The ratcheting crimpers are the the best, but but the price can be a bit high (I just found one on line for $200). But for normal home use you can also get by with a GOOD pair of professional crimpers. I have an old Klein hand crimper, but you can find them at any most any Home Depot or Lowe's. Klein makes professional tools for electricians, so they have them in the electrical tool section.
The Klein crimpers are pretty much a big pair of pliers that allow you to put a lot of leverage into the crimp. The crimp is wide and has the "peg" on once side that dents in the connector to make the secure connection. They really work very well, and they cost around $20. Admittedly not as good as one of the ratcheting crimpers (I have them for electronic connector - old RS-232 pins - so I do know how much better they are), but they do a more than sufficient job.
I the "old days", I used the typical hand crimpers - you know the kind; they crimp, strip, and cut bolts to length. They never did a good job, distorting the crimped connector, and often times having the wire pull out. Not so with the Klein crimper.
Here are two photos of Klein crimpers and a third of a ratcheting crimper. The first is the good kind that I've been talking about. The second is the typical type of crimper that most people try to use - the ones that don't work very well at all. (Note that the photos are not to scale - the first one is bigger and much more heavy duty than the multi-purpose tool in the middle.) The third photo is a generic ratcheting crimper - sells for around $20 (note that it squeezes the crimp but doesn't "dent" it).
An old post I know, but obviously a good crimping job requires a good crimper and proper technique but also a good butt-connector or whatever connector you're crimping. I've bought some before that have a cheap plastic sleeve that seem to "break" when I crimp them and slide off easily... is there any brand you order online or do you have a shop nearby that you get them from (home depot, autozone, etc). I tend to pick them up wherever I happen to be at... whether it be walmart or autozone