I've had recent good experiences on LNER, both north and south between York and Dundee, on both occasions a Tuesday during the day. Served from the "Dish" Menu. (Off topic, but it's surely time for them to refresh the choices on there - they've been in place since the first week of January - not great for any regular passengers). I was perhaps fortunate with the crews I had, but found there to be a very regular supply of complimentary refreshments etc on both legs.
I don't actually mind the seats, despite the complaints of many others on their comfort. For me, there is plenty of legroom / space (and this is speaking as being probably one of the most sizeable forum members!)

Also I have rarely encountered problems with wifi / charging facilities / seat reservations. Usually clean, with decent toilets and regular cleaning up and litter collection. I will criticise the poor amount of luggage storage - particularly for larger bags / cases - this seems to be a problem in standard as well as first, however.
The ambience will of course depend on who is travelling. I find there seems quite a lot of leisure travellers nowadays (some of the advance tickets are very fairly priced), and not quite so many who appear to be on business. I have on a couple of times hit the odd hen / stag party but even then it's not been especially raucous on board.
So overall, based on my own experiences I would recommend LNER First Class. It's definitely improved in the last eighteen months or so, particularly with their weekend offering. Most recent trips were 18/04/23 11.55 YRK-DEE and 25/04/23 11.09 DEE-YRK.