I've played with both, and I can definitely say the bulky dd set is better. Fire/Dragon is a pretty cool defensive typing and with access to roost, he can even set up on shit like defensive rotom-w, which is usually considered a check to char-x.
The biggest problem in my opinion is lando-t. He has great bulk, an intimidate to neutralize early-game set ups, and an earthquake that simply KO's you. It's a weird option, and probably not worth it, but Hp ice may be worth looking into.
0 SpA Mega Charizard X Hidden Power Ice vs. 252 HP / 4 SpD Landorus-T: 260-308 (68 - 80.6%) -- guaranteed 2HKO after Leftovers recovery
That's a solid chunk of damage for such a common pokemon that's used to practically keep every physical attacker on a team at bay. It makes for pretty decent lure and you can definitely wear it down to that range of damage (2 switch-ins to SR does it). The biggest problem to most teams based around a physical sweeper is more often than not lando-t (or rotom-w, but char-x isn't that worried about it). Lando-t is actually just so damn common and luring him in with an hp ice on something that usually doesn't run it could be nice to open up your other sweepers.
This isn't really a great option cuz you're not terrakion who could function with just CC and stone edge if it wanted to, you have a need for moveslots and have superior options, like dd, roost, earthquake, and even SD! (ninja'd on that one, thought about mentioning it but eh), but if you really hate lando-t like I do, I think it should be mentioned somewhere.
As for an actual option, I think thunderpunch is definitely a cool alternative over earthquake. Most heatran have to scout for earthquake, but thunderpunch is lesser seen and allows you to get past azumarill, one of your greatest counters. Getting past azumarill is basically the only reason to use thunderpunch, as dragon claw hits bulky waters a little stronger. But defeating azumarill is very important, as an azumarill might think he can belly drum on the switch or something else bad. If you have trouble with azumarill more than heatran, thunderpunch is definitely a considerable alternative.