I disagree, City's better if you're coming from Europe, but Heathrow still the best airport to get into London from anywhere else, especially Terminal 5. T5 had a lot of problems when it started, but now it's by far the best major airport terminal I've flown from.
It takes me less than 15 minutes to get from the T5 tube station to sitting in the departure lounge waiting for boarding. It's almost as good as Eurostar.
(Although if you're from outside London it can be easier to get to Gatwick transport-wise)
I agree that T5 is pretty decent. The queues are short and there's lots of seating. Access by car is pretty decent if you're on that side of London (which most of the country is). Pretty much all I care about.
I generally try to avoid Heathrow T3 though (and T2 and T4 never seem to have flights to where I want to go).
T5's not awful, or anything, except for one thing: power outlets, or, actually, the extreme lack thereof. There are very few places you can sit while simultaneously charging your laptop and keeping an eye on the departure board.
It takes me less than 15 minutes to get from the T5 tube station to sitting in the departure lounge waiting for boarding. It's almost as good as Eurostar.
(Although if you're from outside London it can be easier to get to Gatwick transport-wise)