I can say that in a poorly configured cluster, I've absolutely seen downtime exceed that of if we had just let a standalone sh**box run itself into the ground instead.

If you can, try to orchestrate a solution that involves load balanced redundancy instead of clustering. Clustering only protects against physical failure, and only when everything is configured correctly. A better solution is to have multiple separate hardware performing the same task and intelligently balancing between them. That way you can take one down with no fuss.

Of course, ideal solution is to have both options set up. But if I had to pick and choose, I'd prefer load balance over clustering.