If it's simply a question of economy, a single will be cheaper to own than twins every time. Less fuel (not a lot less, but measurably less), cheaper maintenance and repairs.
IMO, I want 2 only if I need the safety factor, or because a single engine option would be underpowered.
I would have chosen a single big motor over my twins (both in the current boat and my previous 27' Four Winns) if I'd been able to find a good one.
My .02