To disclose, or not to disclose, that is the question.
Disclosure means potentially killing the relationship before it starts and them not getting to know who you are up to the point where being trans won't matter to them. Non-disclosure could result in feelings of upset, betrayal, anger, even violence if they find out further down the track, especially if they find out from someone else.
Personally I couldn't stand trying to hide something like my status from a potential lover. The fear of being found out, or wondering when I should tell them, would just suck all the fun and joy out of the relationship.