Bristol Airport has an on-site Car Rental Centre, and for a certain kind of trip hiring there is clearly the right answer. For another kind it is a week of paying for a car to sit in a hotel car park. The split is not about cost per day — it is about what you do once you have arrived.
Hire a car when the trip is the driving
If you are touring — Cheddar Gorge, the Mendips, the north Devon coast, a run into Wales over the toll-free Severn crossing — you need a vehicle on hand and a transfer makes no sense. Same for a multi-stop work trip across the South West, or anywhere rural where getting between villages is the whole point.
Take a transfer when the destination is the trip
If you are going to one place and staying there — a hotel in Bath, a conference in the city centre, a wedding, a weekend in Bristol itself — the hire car does nothing between arrival and departure except cost money and need parking. Bath in particular punishes drivers: the city is heavily park-and-ride oriented, and central parking is expensive where it exists at all. See the Bristol Airport to Bath transfer.
The costs that are not on the daily rate
A hire quote is rarely the number you pay. Budget for fuel, the excess or the waiver that removes it, any young-driver or additional-driver fee, and parking at the other end for every night of the stay. Add the two slots of your own time spent at the rental desk — once on arrival after a flight, once on departure while watching the clock.
There is also the return-day arithmetic. You have to get the car back, refuelled, in time to check in. That is the leg people underestimate, and it is why the last morning of a driving holiday so often starts earlier than it needed to.
What a transfer fixes, and what it does not
A private transfer gives you a price agreed before you travel, a driver who meets you inside the single terminal with a name sign, and 60 minutes of free waiting after landing if the flight is late. Nothing to park, nothing to refuel, nothing to return. What it does not give you is a car for the middle of the trip — so if you need one for two days out of seven, hiring locally for those two days often beats hiring at the airport for all seven.
If you were mainly weighing hire against leaving your own car at the airport, that is a different sum — see parking or a transfer and the drop-off and pick-up charges. Otherwise, browse fixed-price routes from BRS.