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)