STATS:
Salamence's BST is 600 and its stats are 095 in HP, 135 in Attack, 080 in both Defense and Special Defense, 110 in Special Attack, and 100 in Speed.
Dragonite's BST is the same as Salamence's and its stats are 091 in HP, 134 in Attack, 095 in Defense, 100 in both Special Attack and Special Defense, and 080 in Speed.
MOVES:
Salamence can learn Normal-, Fire-, Electric-, Flying-, Psychic-, Dragon-, and Dark-type moves through level-up. It can learn Normal-, Fire-, Fighting-, Ground-, Flying-, Rock-, Ghost-, Dragon-, Dark-, and Steel-type moves as TMs. It can also learn Normal-, Fire-, Water-, and Dragon-type moves as egg-moves.
Dragonite can learn Normal-, Fire-, Water-, Electric-, Flying-, and Dragon-type moves through level-up. It can learn Normal-, Fire-, Water-, Electric-, Ice-, Fighting-, Ground-, Flying-, Rock-, Dragon, Dark-, and Steel-type moves as TMs. It can also learn Normal-, Water-, Dragon-, and Steel-type moves as egg-moves.
TYPING:
Both of these two Pseudo-Legendaries are Dragon/Flying-types: which makes them immune to Ground; resistant to Fire(1/2), Water(1/2), Grass(1/4), Fighting(1/2), and Bug(1/2); and weak to Ice(4x), Rock(2x), Dragon(2x), and Fairy(2x).
By stats, they both have the same BST of 600. Salamence has a higher HP stat, Attack stat, Special Attack stat, and Speed stat than Dragonite does. Dragonite has a higher Defense stat and Special Defense stat than Salamence does.
By moves, Salamence can learn 7 different type of moves through level-up compared to Dragonite's six. Dragonite can learn 12 different types of moves as TMs compared to Salamence's ten. Both can learn 4 different types of moves as egg moves.
By typing, they are equal to each other.