Personally I've elected to have only day 5s. The reasoning is that the failure rate with day 3 is higher, but that corresponds to the rates of getting a day 3 to day 5. I'd rather not have a transfer and not get my hopes up than have one that has no chance of making it. Other people prefer the "rather in than in the bin" philosophy, and would rather have something transferred than nothing. It's very much a personal choice.