Make sure you replace *both* wires, not just the broken one. I had foolishly only replaced one and then 2-3 months later the other broke. It's not a horrible mode of failure, but hard to immediately (especially the first time.) At least for me I was getting erratic failed prints because it would connect electrically in some printer head configurations and then die in other places.

Personally I used the decent teflon coated wire I got from a replacement heater I once bought, and for other wires that died (thermistor) I used (quite overkill) some thin silicone-covered multi-strand wire from hobbyking.com.  If your printer is an earlier printer, contemplate replacing all the wires on the extruder head, since the relative work to replace the wires is less than some time later diagnosing the same problem and replacing the wires again. (My thermistor wires died approx 5-6 months later. Both failures after at least 6 months of operation, probably more like a year.)

Also, I kept the same connectors as stock. They were knife-connected in the sense that it's a wire that is just pinched by the connector housing. You can contemplate reinforcing that with solder but it's only helpful if the connectors aren't working at they should.

(The approved list had quite a few of them)