Who sells the best coax crimper and fittings?
Fortunately most crimping dies are getting standardized, I prefer crimp tools that use dies as one crimper handset can be used with lots of different types of dies. I use ratcheting crimpers with the little release lever in case I ratchet onto something bad (like the webbing between my thumb and fingers, it happened a long time ago and I still am in therapy over the incident <joke>).
A very popular (and fairly inexpensive) crimper die style looks like this; http://www.dcpwr.com/shop/images/Assortment,Crimper%20Dies.jpeg
There are many companies that make the crimper frames (handset) and the dies. Typical frames (handsets) may look like this; http://www.pbase.com/image/94464268.jpg
The next step up (in price, 2-3x more) would be something like the RF Industries (the same people who make the Unidapt kits). These are sold in kits with varying numbers and assortments of dies; http://fieldcomponents.com/graphics/00000002/RFA-4009-206.jpg
I am less impressed with the crimpers from Times Microwave (like for the LMR-400). They are non-ratcheting so you can end up with inconsistent results; http://www.ripley-tools.com/IMAGES/Cablematic/CT240.jpg
Times Microwave brands it, so do other companies.
I own all three types of crimper styles, with a variety of styles, from a broad spectrum of manufacturers. I am partial to the RF Industries tools but I only want to buy a tool once and the cost of me going back out to fix a bad connection will pay for the right tooling. If I was in it only as an amateur I would go for what is affordable and gives repeatable results.
Cable prep with proper stripping to the right dimensions, no stray little pieces of shield or foil that is going to short things out. Not getting crazy with too much heat on the center pin (if you solder a PL-259 instead of crimp it) and taking your time to do it right will really pay off.
Crimped connections can get a bad reputation, usually it is the wrong type of crimper tool, bad technique or really cheap connectors. I do not suggest going for the $1.09 connectors sold in a giant bag, it is penny wise and pound foolish.
You did ask about "the best". Not the cheapest or the fastest.