A lot of players say, that physics in TSC is better than in TSW. In what way is it better? Im not sure about this point... Can anyone explain it?
Depends. TSW offers a much more detailed physics system, as the locos are almost assembled like a real loco, google for SimuGraph blueprints. The downside is, troubleshooting is extremely difficult. You're building the loco from the ground up and then hope it behaves right. TSC physics are easier, they're top down. A set of fixed parameters that must be tweaked so it behaves as expected. Additional scripts can give excellent results, Smokebox's steam locos have to be mentioned here. Something not achievable in TSW. The outcome can be realistic in both cases - if set up correctly, which is harder and more expensive to do in TSW.
The lua scripting angle of TSC appears to offer a lot more flexibility too. I'm not sure if random power, brake or even cooling fan factors are possible in TSW.