After many (many!) years of doing this to servos and speedos, the best method is the crimping tool by a country mile.
In that time, I've managed to make intermittent connections with the pliers method, melt miles of cable sleeving with a soldering iron, create soldered pins that no longer fit into the plug, and ruin two servo circuit boards! Since I bought my crimping tool I haven't looked back. It takes a couple of attempts to get the knack of it, but it gives a perfect joint, that fits the plug, every time. HTH
