Ask HN: What visa should entrepreneurs apply for YC

If a foreign entrepreneur is applying for YC, What type of visa, should He/She apply with the consulate?

If the founders are called for an interview, can they use tourist visa, or is it considered as a business trip?

If founders are accepted into the program, what type of visa should they get, for the 3 month period in the valley?

Founders who had been through, this process, please tell your experiences.

Thanks.