Pre-T, I preferred men as I felt that they would be more likely to see me as a male (before I passed). Considering that 99% of the time when I was simply presenting as male, only men gendered me correctly.
Today, because I pass 100%, it's not an issue - but I still feel uncomfortable if a doctor finds out that I'm trans no matter what their gender. I would probably prefer a woman at this point in my life if I had to disclose my trans status to a doctor - I find that female doctors have seemed to be the most understanding once they find out. A few male docs I've seen have given me a sort of sideways look.