From personal experience they both have their positives and negatives. What I did was play a career with GW then installed NYGM and am play a career with that. Try em both, you wont be disappointed.
As far as what make NYGM more hard core? For me its the no gods eye veiw. I can no longer use the map screen to tell me which way the ships are moving and which ones are merchies or warships. I have to actually spend some time on the bridge figuring that out for myself. And I gotta tell ya, it sux at first but becomes VERY gratifying when you get the hang of it.
