In my mind HD is a superior product and there's really no comparison between it and GD.
For identical cost, the HD season is considerably longer, so you're getting more game play for your dollar. The AI in HD is far superior -- very rarely do you see something happen in HD that strains the bounds of credibility or believability, whereas, at least when I stopped playing, GD was producing things of that nature with glaring regularity (timeouts with seconds to play and the ball deep in your own end of a tie game, allowing for a game-losing safety...timeouts before game-winning FG attempts that left enough time on the clock for the other team to run back a kickoff for a TD...quarterback scrambles up the middle on the final play of the game where a hail mary to the endzone is the only plausible play call...and the list could go on). Lastly, the crew at HD is generally good about providing feedback. Yes, there are issues we've clamored about with regard to recruit generation, but even at the worst over here at HD, it was nothing like the steaming black hole that GD was sucked into. I understand through the grapevine that things have improved slightly with norbert having replaced jconte on the project, but for me the damage is done and it will be a long time, if ever, before I put more money into that product.