Don't get me wrong, but unless you're hell bent on that moveset, it isn't really the best for M - Garchomp.
Anyway, to answer your question:
Dual Chop is better.
The major reason is due to the poor accuracy of Dragon Rush, because, at 75, it only just better than Focus Miss. Even though Dual Chop is weaker, it breaks, as you said, Substitutes, as well as Focus Bands/ Sashes, and abilities like Sturdy, which is a major advantage of Dual Chop.
Also, in case you do want to change your M- Garchomp's moveset, look here for some really good ones.
Here's an example:
Mega Garchomp (M) @ Garchompite
252 Speed/ 128 Special Attack / 128 Attack
[Hasty +Speed -Defence]
- Draco Meteor
- Fire Blast
- Iron Head / Stone Edge
Edit: Sorry, didn't read your question properly: I suggest using Swords Dance + Dual Chop over Hone Claws + Dragon Rush because it takes while it takes only 1 turn for Hone Claws to set up enough for Garchomp to not miss Dragon Rush at all (at 99.75%), it still doesn't break through other Substitutes/ Sturdy Pokemon.
However, Hone Claws Dragon Rush is still a viable option, but be aware of your opponent's Pokemon.