To be honest, you'd be much better off with Fire Punch rather than Heat Wave or Flamethrower, because Dragonites are more physical oriented, but if you want a good Fire special move that even works in double battles, I'd honestly go for Fire Blast or Flamethrower, because usually, hitting two pokemon at once in a double battle, isn't as much effective as hitting one, because moves that hit multiple Pokémon have their damage reduced by 25%, unless all other Pokémon have fainted at that point.
In doubles, sometimes hitting both opponents is a benefit, despite the reduced damage. This is why some Pokémon run Rock Slide over Stone Edge, Heat Wave over Flamethrower/Fire Blast, etc.
But other than that, I agree; Dragonite is better off with physical moves, as its Attack is marginally higher than its Special Attack. It can even go mixed in Rain if it has to. Just make sure its ability is Multiscale, as that ability is what makes Dragonite so good in OU:
-Dragon Dance
-Outrage/Dragon Claw
-Fire Punch
-Roost/ExtremeSpeed/Earthquake
Nature: Adamant/Jolly
EVs: 252 Atk/4 SDef/252 Spe
Item: Leftovers/Lum Berry
Ability: Multiscale
or
-Outrage
-ExtremeSpeed
-Fire Punch/Waterfall
-Earthquake/Superpower
Nature: Adamant
EVs: 4 HP/252 Atk/252 Spe
Item: Choice Bnad
Ability: Multiscale
or
-Substitute
-Dragon Dance
-Dragon Claw
-Roost
Nature: Jolly
EVs: 252 HP/72 Def/60 SDef/132 Spe
Item: Leftovers
Ability: Multiscale
or
-Substitute
-Thunder Wave/Flamethrower
-Dragon Tail
-Roost
Nature: Careful
EVs: 252 HP/4 Def/252 SDef
Item: Leftovers
Ability: Multiscale
or
-Draco Meteor
-Fire Blast/Flamethrower
-Thunder Wave
-Roost
Nature: Modest
EVs: 252 HP/252 SAtk/4 SDef
Item: Leftovers
Ability: Multiscale
(last 2 sets are for rain only)
or
-Hurricane
-Thunder
-Aqua Tail/Superpower
-ExtremeSpeed/Earthquake/Roost
Nature: Mild
EVs: 76 Atk/252 SAtk/180 Spe
Item: Life Orb
Ability: Multiscale
or
-Hurricane
-Thunder
-Dragon Tail
-Roost
Nature: Calm
EVs: 252 HP/4 SAtk/252 SDef
Item: Leftovers
Ability: Multiscale