Just to reiterate what people have said above crimping is the way to go when done properly. Crimping is the preferred method for the harnesses that we build for motor sports. Take a look at the contacts for Mil-spec connectors and Auto Sports. They are all crimp termination. The rare instance that I use solder when building a harness is when I am terminating a shield on shielded wires but I do that with the RayChem solder sleeves with the pre-installed lead. If you would like pictures of how some of the harness are built let me know and I can up load some.