Your question is very subjective!!! Personally if your into building or modifying routes, I'd recommend Trainz a New Era build 105766 SP4, because it still has an "Undo" button that has easy access. (in Tane surveyor, I use the "Undo" button, more than any other button in Trainz)...
If you are more into running trains on routes (sessions) then I personally would run with TS2019 PE 111951 SP3.
I hope this helps.
Cheers, Mac...