If you're look at it for RP purposes....
"It's good to be Champion!"
No but seriously that line almost singlehandedly convinced me to be Champion, definitely the coolest specialization dialogue for warriors. However I already have Cassandra in my party for RP purposes and am a 2H warrior, so I felt that Reaver would be the best option.
All that aside, with SnS, on normal, either build is very viable. Champion can make you an unkillable tank, SnS is already nigh unkillable regardless though, so if you want some more damage, particularly against demons+barriers, at the cost of literal invulnerability from two Champion skills, then Templar is a good tradeoff. Mind you that they have an AOE stun with an AOE Eldritch detonator.... so Templar can seriously lay down the hurt.
I feel like people talk a lot about Reaver (risk/reward playstyle, high DPS) and Champion (unkillable, literally) a lot but don't mention Templar, but it's a very valid specialization.