Wifi on Grandeur last winter was pretty bad. Had to roam the ship looking for decent reception, usually near the centrum or toward the back near the diamond lounge.
That said, we loved the ship overall and will be there for 10 nights next winter. You can step on an elevator without waiting 10 minutes or packing in with 10 people. Windjammer isn't packed and chaotic. Deck chairs are available. We got on Symphony after Grandeur: Windjammer packed beyond belief, elevators a nightmare all day and all night, people laying on the floor on upper decks because loungers full at 7AM. We'll never do Oasis class and larger again.