In 1st, not only are the seats wider and otherwise more spacious but you tend to have a better class of person travelling. (Me an exception

).
Outrageously snobbish but it made me laugh

I love it
Visiting last year, I found the attendants on GWR were OK, but not quite as proactive as Avanti WC ones.
Weakest 'free food and beverages' was on TransPennine Express.
On a strike day when Grand Central operated (thank God), attendants were friendly with food offering 'medium'.
Avanti West Coast definitely offer a better service, but one might say that the offering has been considerably downgraded since taking over from Virgin Trains primarily to facilitate the introduction of Standard Premium. Four first class carriages on 11 cars became two, or three became one on 9 cars, and one of those cars is the tiny kitchen car - which while typically my favourite due to added privacy and better tilt going south - is regularly used abominably by lazy crew on southbound runs as a place to chat and eat the rest of the food - they’ll rarely leave their seat again after Crewe or Coventry despite ninety minutes of expensive journey remaining. They’ve reduced complimentary hot food options considerably too, used to have three choices at dinner.
LNER are largely the same, either slightly worse on services offering the Deli menu, and slightly better on services offering Dine. The messroom issue isn’t as bad but still exists on Azumas. Their London crew are shockingly condescending and can treat you like a schoolchild if they don’t take to you…
TransPennine, TfW and Grand Central will give you snacks only. GWR will give you snacks too but far more choice, and they tend to serve you multiple rounds. Often TPE’s won’t be available though, especially on 185s.
CrossCountry will give you snacks only on 170s with catering, but a wider range similar to GWR’s is available on Voyagers - plus sandwiches, hot bacon rolls and muffins which GWR don’t do. They used to do hot meals on some North East South West services but I believe these are no longer available, and often weren’t during their run anyway. Hull Trains have a similar menu.