I'd say hire the one that gives you the best justification for their estimate. It's important for people to understand what is and is not involved in an estimate as well as why they think something is hard.

Once you communicate that, you can uncover a lot of potential problems and misunderstandings. For instance just the other day my co-worker was asked to estimate a task that seemed to our boss to be pretty small. He estimated it as being 2-8 days, it wasn't until they actually started talking about _why_, that they both agreed on the requirements. The resulting task will probably take 1-3 hours.

So sure, as a developer learns more they may estimate tasks as being longer, but communicating your assumptions is more important than throwing out huge estimates to cover your ass ;)