Newquay Airport has a lot of real estate, much of it on the western side which was the old
RAF▸ St Mawgan is still "behind the wires" as far as i know.
Easily a long-enough runway for anything currently flying (witness the
BA» 747's that recently arrived for part-out), so expect to see the
USAF▸ transports carrying "The Beast", the Marine and Army helicopters used to transport
POTUS▸ and his security details all heading for there I would expect.
Culdrose is smaller, but it's 6000ft main runway more than adequate for small/medium-sized transports, and lots of secure Royal Navy hangars for the US helicopters to hide away in/have any required maintenance done, for example.
I think you can discount
LEQ» (Lands End Airport), short and narrow runways there, which are fine for the Skybus Twin Otters but not for anything much bigger.
"Air Force One" would be something much smaller relabelled for the occasion
"Air Force One" is a callsign, not a specific aircraft. It is of course mainly used by 1 of the 2 747's built for the job that we all recognise, but can be applied to other aircraft, as it was when Trump departed from Southampton in a C-32 (a VIP Boeing 757, in it's US military guise) last year.
The venue for the summit is reportedly Tregenna Castle, which makes more sense from a size and security perspective than other places that had been mentioned (eg, Carbis Bay Hotel).
The "hassle factor" of having this global circus descend will mean some disruption to local life, for sure, but will surely be outweighed by the income (already estimated at GBP 50m) input to the local economy, which must be great news, along with the publicity it will bring for Cornwall in general.