Depends on what you need. Xander is a DC unit with decent attack and high defense, not to mention can benefit from Cavalry buffs. Nino is an infantry Bladetome user that can "potentially" nuke the enemy team given the right skill set and IVs. Normally, people want to go for +Speed on Bladetome mages, so...
Who to 5 star
I'm looking to five star another unit once tempest trails come out, it's currently between xander and a -hp +res nino, thoughts?