Sadly but true , Serperior has a shallow moveset and the fact that she(along with Samurott) can't learn Earthquake like the other starters(Swampert and Torterra learn it by level up) can , therefore adding insult to injury(good job gamefreak >_<) . All I can hope is that she gets a moveset upgrade in the future ...
Typing-wise , Swampert wins since he only has one weakness and Serperior is a pure-type like Sceptile and Meganium.
Hidden ability , Serperior wins , because her ability is beneficial , unlike Swampert's Damp , which is useless , especially with the nerfed Self-Destruct and Explosion ..
I prefer Serperior's design to Swampert's ... Serperior looks much better , another reason why I prefer Snivy to Mudkip .