Hitachi
They work well but I'd rather support Bombardier's factory which is more permanent than Hitachi's build-it-to-win-the-IEP assembly plant. They would work fine, commonalty with the 395s isn't important, both fleets are large enough (and different enough) on their own. Not also the greatest of quality from Newton Aycliffe
Bombardier Aventra
It works when it works, software has been a problem on the Aventra for a while... Quality from Derby is typically worse than other manufacturers. Commonality with the 375s is nice, I can honestly see the 376s getting dumped though, shown by the lack of refurbishment or repaint.
Siemens
Very reliable units, just need to change the seats, has the benefit of supplementing the 707s. Will also soon have a factory in the UK which will score political points.
Stadler
Level boarding is a major plus but they aren't cheap.
Whoever it goes to somebody will be annoyed, despite still being built in the UK some politician was annoyed the EMR Intercity train order went to Hitachi instead of Bombardier.