All Depending the current flow, workmanship and material used.

Is your contractor using good crimping & connectors material and tools? There are good crimps & Connectors and workmanship is important. Those using the simple screw time, i find it useless especially in high current usages. The good ones are like butt connectors from 3M, AMP, and many others. But all these are costly to your contractor, one connector can cost RM1-2 each.

Solder is easier (in my personal opinion), proper prepare the wires, solder it, double heat shrink wrap. done deal.