Depends on what we are doing. We live in Bedfordshire, 30 min from Luton Airport, 40 min from Stanstead, 60 min from St Pancras International or 6-7 hours drive door to door.
We tend to use Eurotunnel as we often get one or two free crossings with our Tesco's clubcard points, plus you can load the car up there and back (we're taking a crate of coke, a crate of milk and a crate of water from Costco - 50p for a bottle of coke as opposed to DLP's £2.30!!!). On the way back we do our grocery shopping (and some wine) as virtually everything (inc washing powder) is cheaper in France. We can also buy anything we want from DLP then.
I hate flying there as it takes as long as flying between the security at both ends and the dreaded (and expensive bus).
If it's a short trip, then we go Eurostar.