Salamence is better, but Dragonite can use stuff like Thunderbolt, Thunder Wave, Ice Beam, Focus Punch, Agility, etc. that make it a worthwhile choice. It's too bad that its defenses don't really matter so much since it'll just get Ice Beamed or whatever anyway.
Dragonite has always, and always will be my favorite dragon, it just seems so unique from the other blander dragons. Plus it can do a lot of things Salamance can't, like use the elemental punches, boltbeam and SubPunch.
Let's see, Dargonite has more defensive, can have a good defensive set "with Roost, Sub , dragon claw and Fire Punch"....can be a hazer....also can learn DD...which is if it had good HP EVs and SPD EVs...it'd be last and be fast enough to sweep....on the other hand...Salamence is just pure sweeping with good speed...either special or physical.
Both are killers. Dragonite`s attack is better but Salamence is faster, that why it has bigger chances for winning. I had a battle to someone and my Alan (Gastrodon) lost because was slow. That battle taught me something very important: faster pokemon wins- that why my vote goes to Salamence.
Salamence is better in battle. He has stats much better suited to what he is for, sweeping. Dragonite is also a sweeper, but his stats aren't as good in that as Salamence. Really the only big thing Dragonite has that Salamence doesn't is enormous movepool. Salamence does have a good movepool anyway, but it doesn't match Dragonite's.