The Hilton is in the south terminal at Gatwick, which is very convienient if you are flying with Virgin as it's very close.
The parking is now a bit of a pain apparently, If you booked with ABC Holidays Extra you now have to park in the north terminal car park which is about 20 mins away. If you booked directly with the Hilton you will end up in the south terminal car park, which of course is much closer.
The Hilton costs a bit more, but because it's in the south terminal and close to Virgin, which in turn, means its very easy to use twighlight checkin, to me it's worth the extra.