Thanks for all the reply. I didn't know that First Class was different from airline to airline.

I will be flying from San Francisco to Hong Kong.

I will be flying on Cathay Pacific most of the time but will also fly on United and China airline. I will be using Mileage for business class but just wondering if the extra mileage is worth it to get First Class instead of Business. The flight will be about 13-14 hours and I hope I will be sleeping most of the time since I usually pick early morning flight around 1am or so. Thanks