Personally i prefer newer timetables, as it uses stock that I'm familiar with, however as it has been said, earlier timetables have greater variety, and i personally think they're more challenging, so (in my opinion) are better for multiplayer games.

Meyshollop

For me I prefer the newer timetables, well at least until I get to know all the locations on the sim. With their simpler MUs and fixed formation trains you get a quicker feel for the sim and it's entry locations. After that it is easier to move onto the more complex older timetables with their engine changes/run rounds and varied freights that were around in those days.

The older ones for me. Although I'm just as happy playing the modern era TT's and settings, the 70's, 80's & 90's was my time having joined the railway in 1987 and been interested since I was a child and can still remember visiting Swindon Works in the school summer holidays when it was still open. The older TT's bring back memories of long forgotten locos and units that I used to love travelling in or being hauled by.

Well, I'd love a Western Region TT set in the era when hydraulics were in use

I love them, however, I've never seen one in real life as I live in Hungary.

I will use either. As long as it is "robust" and workable.
However, I do prefer the older ones. With loco's to run-round and stock to shunt.