Sometimes on site short term can be ok on price if you book it in advance, although peak holiday time may come at a premium. Mostly I tend to use on site long term. Short bus ride to terminals, pretty efficient service and not too expensive if you pre-book.

I just use this - official parking. Gives you options. I won't use private operators meet and greet or off airport parking.

www.heathrow.com/booking/parking

Usually end up with long stay, which is really no different to business parking - for 2/3/4 it's just outside the perimeter road rather than inside. Occasionally business parking is within £5 the same price in which case I use that - in theory the buses are slightly more frequent but in practice it doesn't seem to make any difference.

Book as soon as you can, half term will be expensive regardless.

I've used these guys before and never had any problems (even when leaving them with a new 3.2l Audi convertible).

I have used both of their services in the past (park and ride and meet and greet) and both were efficient.

www.purpleparking.com

Sign up before hand for a 15% discount voucher.

I used a park on the drive service twice, once in Central London and another time near Hounslow West which is on the Heathrow tube. You need to read the online info and any pictures (including Streetview) and reviews carefully to ensure it’s a viable safe space. The Central London one was a tight underground car park, OK for my Civic but a big car would require a lot of manoeuvring and might have been vulnerable to other cars as the space was not big.
The Hounslow drive was offering space for three cars but when I got there the two people ahead of me hadn’t left enough room for a third car. To be fair it was very tight for them to have done so. Luckily the householder was there and moved his own car so I got in but I wouldn’t have liked to arrive there when he was out and I had a plane to catch.

Personally, for Heathrow, I would stick with the official on airport but if you opt for a driveway do your research into exactly what is on offer and be wary of anything that isn’t a clear marked single space.