Easy. I say free gas for 20 years. For flights, I'd still be responsible for hotels, food, etc..while on a trip...not to mention not having enough PTO to enjoy it. The car would eventually need maintenance. If I had more time, I could coupon and reduce my groceries and not need the grocery stipend.
Gas, hands down! We would likely buy a new boat and RV while we're at it and totally enjoy all things gas-guzzling! DH really wants both (and we'll likely get at least an RV since that's what we both want) but most likely isn't happening until retirement.
DH hates to fly and is too cheap to spend money on hotels, etc. We don't need a Mercedes and we don't spend $300/month on food even though I cook pretty much every meal. $300/month in gas is pretty close to what we spend and we watch where we drive to keep that cost down...not having to worry about how much we spend on gas would be awesome, especially since we are road trip type travelers
Gas hands down, DH and I would travel the US and Canada. We could camp along the way to make that cheaper. (If gas wasn't an issue would would travel with our trailer, so we'd have a fridge and so food wouldn't cost more then normal either.)
So really gas would give us the travel and we eat anyways so that wouldn't change much.