I travel regularly from both airports. Living in central London I find the journey to Gatwick much more convenient.
When flying point to point I feel Gatwick wins. It does however have limited route coverage, but this is increasing all the time. Gatwick has improved a lot over the past few years. But I am afraid it will always feel like the poor relation to Heathrow.
If I need to tranfer flights in London then Heathow is my first choice. I find it very impersonal and a bit of production line. But is really set up for conneting between flights.
If I have chioce I prefer Gatwick because of its excellent rail links to London.
I hope that Gatwick continues to attract more airlines giving us the passengers greater choice.