We've stayed at the Mercure 3 times and loved it. We love the relaxed vibe, huge beachfront with lots of trees and how the buildings are spread out amongst the gardens. The first time we stayed in a Deluxe room and it was very nice, but we tried the superior room the next time and stayed in that same room (overlooking one of the pools and fairly close to the beach) 2 years in a row because we enjoyed the view and location so much.
We prefer staying in the southern end of Sanur and had previously stayed a few times at the Puri Santrian but didn't want to spend that much on accommodation. The Mercure, whilst not of the same standard, was good for the price. We're also Accor members so we get points for staying there. Let me know if you want further details.
From your shortlist I suggest the Mercure.