I think it’s hard to judge a “favourite” when, functionally, different TOC’s provide very different services:
For intercity TOC’s, LNER would have been my top choice if it weren’t for their shockingly poor customer service and attitude towards COVID messaging.
VTWC would have also been up there, but Avanti have totally ruined what used to be a good franchise, and I can only hope they will redeem themselves with the 390 refurbishment due out soon.
GWR are relatively good, but their first class offering is far inferior to LNER’s and Avanti’s. I also find the lack of a buffet car on the IET’s hugely disappointing.
TPE have very nice new stock, and their reliability has certainly improved recently, but again their first class offering doesn’t come close to LNER or Avanti (although, given their use of nicer stock and plug sockets, I would choose them over Avanti for any WCML journeys in standard at the minute)
Scotrail have the potential to be really good, but are completely screwing this up by:
Refusing to sell any advances
Maintaining a blanket alcohol ban far longer than needed
Their very aggressive covid messaging
Their pathetic “emergency” timetable (last services, particularly on Cathcart circle, are ridiculous!)
NO catering offer on any services. The HST’s have perfectly good buffet cars, which should be open.