So I'm probably opening up a HUGE can of worms considering how heated this debate was back with the PJ trilogy first came out. But fun fact, the Arwen/Eowyn debate has been going on far longer than that, since the books were published. And according to TVTropes, originally Aragorn WAS supposed to end up with Eowyn, only for her to die and Aragorn to never love again out of despair. But the Tolkien came up with Arwen (who doesn't even show up except in the appendices) and paired off Eowyn with Faramir. Apparently for years Tolkien received letters from angry fans telling him how Eowyn was the better match for Aragorn.
Contentious issues as it remains (those flamewars on Fanfiction.net were hillarious) I'm gonna say Arwen was the better pick if only for political reasons. Arwen's people were leaving so Aragorn married her solely for love. While with Eowyn, she was the sister to the new king Eomer, which might have led to problems later on. So yeah, Arwen is better for me. And no, not just saying that because I had a massive crush on Liv Tyler in the 90s, not at all...