Personally, I think that it's a better idea to select a houseguest that will vote against the nominee you want to stay.
So far, the MVP nom has only been evicted 2 out of 5 times, and both were selected by the in-house MVP. I don't think America's choice will ever get evicted, since they would likely be nominated if the house wanted them out....
Therefore, I think the sound move is to try and get a vote against your nominee removed by putting someone up that would try to vote them out.