Its...a tough question because I like the both of them, but, I'd prefer Salamence.
Salamence is not really cute and cuddly like Dragonite, but this dragon Pokémon is my favorite of the two. Salamence looks more fierce than Dragonite (backed-up with his ability Intimidate). Evolving into Salamence is probably one of the greatest moments the Bagon Evolution line can experience. Becoming a Salamence fulfills Bagon's greatest wish: to fly high in the sky. (which somehow resembles my own dream). Salamence is easier to get than Dragonite because Dragonair evolves on Lv. 55 while Shelgon evolves on Lv. 50.
Dragonite probably has easier access to some moves like Dragon Rush, Surf or Waterfall, or even Thunder, but Salamence can inherit cooler moves like Hydro Pump and has access to more useful moves like Crunch. Which in my opinion, I like crunch because its really good against things like pesky Cresselia. ^^;