I've been lucky enough to make a couple of round-trips on private jets in recent months. My conclusions surprised me a little so I thought it would be interesting to compare the experience with BA First (experienced a few times, only thanks to miles!).

The PJ trips were 6 hour flights to some dodgy mid-haul destinations, first on an 8-seater CL-600 from Farnborough "Airport" and then a 12-seater Legacy 650 from Luton (BBA Signature terminal). There wasn't much difference between the two craft (seating, comfort) other than size. I wasn't travelling with friends/family so privacy and space were perhaps more of an issue than if this had been the case.

Pre-flight:

On the PJs, check-in is of course very quick. At Luton they had a desk to visit, but Farnborough went one better simply requesting your passport for a few minutes while in the lounge. You are asked to arrive 45 minutes before departure, of which formalities and boarding take 5 minutes, versus say 2 hours / 20 minutes at LHR. Of course your schedule is more flexible on a PJ.

The lounge at Luton was pretty disappointing. A dull, narrow room with some leather sofas and no view. Farnborough was much better - like a mini T5 view floor to ceiling windows and a view of the apron and airfield. But both only offer coffee - no treats unless you bring your own. Overall, unless you are a jaded traveller or a DYKHOWBUSYIA, I'd prefer to spend 90 minutes in the CCR rather than 40 minutes in these facilities, especially BBA Luton.

Security was non-existent at Farnborough (?) and airport-like at Luton, albeit quicker and private.

All in all, I enjoy my occasional airport visits so BA First wins for me, but in any case if BA could sort out security and boarding (5-10 minutes instead 20 minutes without the hassle) I'd say their experience would win for most travellers. (Though at third-world airports the more-personal handling is a big advantage.)

In-flight:

Both PJs had 1+1 armchair seating, with rows facing one another. This no doubt works well with friends but otherwise you have a lot less space than in First and no privacy. I think the BA seat is more comfortable too. The PJs had no personal IFE.

On our overnight legs, the real problem was you need a pair of seats to form a flat bed, which in any case isn't particularly soft or wide. With a flight more than half full, the option is just a reclined seat.

You get pillows and blankets but no sleeper-suits! Definitely a win for BA First unless you're with friends and, if travelling overnight, only half-full. But in those circumstances you'd pretty much have your own BA First cabin!

Food & drink:

I guess on a PJ you get whatever you order and pay for, particularly wine-wise. But you'd pay a lot to match the BA wine list - it certainly wasn't matched on my flights.

Similarly for food. The more extravagant menu included a very nice fruit de mer which bettered what I'd eaten on BA, but hot options seem to be more technically-limited to curries and similar.

Overall, probably all-square, depending on budget.

Arrival:

Smaller aircraft = quick disembarkation, immigration and baggage retrieval but this may depend on the airport. And your car can usually meet you at the steps! A definite win for the PJs.

Conclusions:

Though it was great fun travelling by private jet, I was surprised to find it definitely didn't better my enjoyment of BA First. The bigger aircraft offer more space and facilities, and some advantages on the ground too.

If BA could improve security and boarding for F passengers, I certainly prefer to fly with them unless it's with friends and an unlimited budget. PJs would only be needed for more unusual destinations and schedules.