For us it depends on a number of factors - cost of all options, length of holiday, which airport we're going to and what time we're flying out (or arriving home). Sometimes a taxi (or a lift from a family member if you're really lucky) works out to be the best option, other times parking up at the airport suits us better - almost always we use the airport's "official" parking provider however.
For our last big pre-Covid holiday we booked a taxi to Gatwick the night before, as we were staying in a hotel cause our flight was really early the next morning and that worked out quite well, although on the return leg they sent a really small car to pick us up and we had to play suitcase Tetris in the pickup area to get everything in!
However for our most recent trip (that we only came back from last week), we parked at Heathrow using their Meet & Greet service as the website quoted it at only £10 dearer than their long stay option - not having to wait around ages for a bus to shuttle us out to a car park that is seemingly 10 miles drive away by road even though it's still on the airport perimeter, was quite nice when you're tired and jet-lagged from an overnight flight.