I am contracting out a service upgrade to 200 amps. Any advice on which brand panel is the best.

Greets Cutler Hammer CB Single pole 15 Amp GFI breaker. Installed per manufacture's instructions. White ground wire on breaker to neutral/grounding buss bar. Neutral circuit wire attached to neutral lug on breaker. Hot wire attached to load lug on breaker. Switched to on postion and breaker tripped immediately. I took the neutral wire off the breaker and attached it to the neutral/ground buss bar. Turn on the breaker and it tripped immediately again. Per troubleshooting guide that came with breaker, possible reason was panel's neutral and grounding buss bar are the same buss(This is the situation with this panel). I did find that the circuit was wired in a way I've never seen though. The circuit is a 14-3 "romex" cable. One hot wire was connected to one 15 amp breaker and another hot wire was connected to another 15 amp breaker. Both circuits "shared" the neutral wire. Trying to get one of the circuits on the GFI breaker because of some new wiring to an exterior application and didn't know for sure where the first "load" was to install just a GFI duplex. What are my options here? Try to install a separate grounding buss bar and isolate the neutral buss bar from the panel? Or am I missing something?