It all boils down to the usage you want to apply to these Pokémon.
While Dragonite has an higher Atk, the rest of its stats are equal to Goodra's, minus that bulky Sp.D, which is what should make you choose the Pure-Dragon 'mon after all if you want a semi reliable wall.
Although keep in mind that other Dragon Pokémon ( namely Hydreigon and Salamence ) can/will cover that position just as well, if not better, due to Goodra's average HP stat of 90 and its only recovery move Rest.
But, Dragonite IS Dragon/Flying and that does bring more weaknesses, that you may or may not be able to cover with various moves and other Pokémon in your team.
It's a tough call, so in the end, it depends on how your team is structured and what Pokémon you feel more comfortable using.
Anyways, Smogon has a Assault Vest set for Goodra:
Goodra @ Assault Vest
Ability: Sap Sipper
EVs: 248 HP / 252 SpA / 8 SpD
- Draco Meteor
- Fire Blast
- Sludge Bomb
- Dragon Tail
It's pretty good honestly!
Draco Meteor is Goodra's most powerful STAB attack, and it hits like a
truck even without a boosting item. However, this attack lowers
Goodra's Special Attack by two stages, and has a 10% change of
missing. Dragon Pulse is an option, providing less power than Draco
Meteor but not having the nasty side effects that come along with it.
Fire Blast hits Steel types, such as Mega Aggron, Forretress and Mega
Steelix, which resist Goodra's main STAB move, for super effective
damage. Flamethrower can be used over this for perfect accuracy but
less power. Thunderbolt hits bulky Water-type Pokemon such as
Alomomola and Empoleon for super effective damage and provides
unresisted coverage with Fire and Dragon. Dragon Tail is useful for
phazing opposing Pokemon that might attempt to set up. Sludge Bomb
hits Fairy-type Pokemon such as Florges and Aromatisse which are
immune to Goodra's main STAB move, while Muddy Water hits bulky
Ground- and Water-type Pokemon. Ice Beam can be used to hit Gligar,
while Power Whip is mainly used to hit Swampert.
An Assault Vest boosts Goodra's already high natural Special Defense
to extraordinary levels, taking even certain super effective hits
incredibly well. Sap Sipper is the ability of choice, giving Goodra a
free switch into Grass-type attacks and boosting Dragon Tail's power.
Maximum Special Attack investment with a Modest nature lets Goodra hit
as hard as possible. 248 HP EVs boost Goodra's good natural bulk,
while reducing residual damage.
Goodra has free reign to switch into the majority of special attacks,
taking most of them fantastically well, which makes it a fantastic
pivot into special attackers such as Chandelure and Shaymin; take this
advantage to hit whatever switches in extremely hard with one of
Goodra's attacks. Be extremely wary about attempting to stay in
against physical attacks, as even with investment into bulk, Goodra's
mediocre Defense leaves much to be desired.
Alomomola can switch freely in to most physical attacks aimed at
Goodra while also giving Wish support. Goodra can also switch into a
plethora special attacks that might threaten Alomomola. Swampert not
only provides fantastic type synergy with Goodra, but it can also lay
down Stealth Rock to help it wear down its foes. Florges and
Aromatisse can provide Wish support as well, as Goodra can get worn
down easily throughout the battle. Mega Aggron has phenomenal physical
Defense, being able to comfortably switch into many physical hits that
threaten Goodra. It can also provide Stealth Rock support so Goodra
has an easier time wearing down its foes.
Let me know if this helped!
Smogon's Goodra page
Smogon's Dragonite page