Coincidentally, that's almost exactly the thought process that I'm going through at the moment for a particular trip. Assuming some sort of pre-Covid service levels, it's:
Depart Newcastle 08:40
irect> Arrive Plymouth 15:47
Or:
Depart Newcastle 08:27 <via London> Arrive Plymouth 16:12
In both cases, I am then travelling on to Gunnislake, so the final arrival time will be the same either way, at 17:20, and it would be in First.
Considerations:
Direct service to Plymouth is with CrossCountry, on a Voyager. First Class service is complimentary 'snacks'.
Indirect service is with LNER and GWR, both on IETs. First Class service would be cooked breakfast on LNER, and then the 13:04 from Paddington is the Pullman Dining lunch train.
Ignoring pricing for the moment, as Advance fares aren't currently available for my intended date of travel, I am erring towards indirect. On an Anytime basis, direct is £380.40 and via London is £387.00, as an aside.
However, if I leave Newcastle an hour earlier, the service to Plymouth would be an HST (again, in normal times). Might that tip the balance towards it?
And what if there's still no catering on either or both LNER or/and CrossCountry. It's getting on for nine hours however you cut it, so does getting on and nesting with multiple picnics and no lugging luggage appeal more than potentially queueing for more supplies in London.
Decisions, decisions!