You want to make them believe that you want to work for their company because it's so wonderful. Don't say anything else about other companies. Besides it sounding unprofessional, it sounds immature.
I think making them think they're your only option would be the best course of action. They want a long-term worker, not someone who will be there for a week and the hurry off to company A.
If you have other opportunities though, they might think you'll bail on them. Just shut up about it. Think about if you were a company.