If someone has: - a full-time job in a foreign country (say, Germany) that sends him in the US on a 2 months mission, - a part-time job in the US (1 day per week), which let him work from Germany but also in the US under a part-time O1 visa (accepted).

How should that person enter the US for the 2 months trip? Under an VISA waiver B or O1 part-time?

Thank you so much for your time.