I am a 21 year old virgin who has chosen to be "deflowered"(god I hate that word) by a professional.  I'm having trouble deciding on whether I should go for one hour or two.  I would like this to be a learning experience, so I was thinking two would be best, but then I read that you should never book over an hour for your first session with a provider, so now I'm torn.  Anyone have any suggestions?

I'd find a well reviewed lady that offers multiple pops.Alot of people may disagree with me on this but if you have the money and the well reviewed lady go for 2 hours. It will give you plenty of time to get comfortable and enjoy yourself.

You are very young and I normally tell guys your age to look into civvy dating before trying the hobby. But after reading post after post by men that rue the day they took on an significant other, my advice on civvy dating may lead you into a situation that you will grow to hate.
So here is some advice that I hope you can use. Find a provider that you have researched and are sure is legitimate. Your choice should turn you on due to her looks, figure or both. Book two hours, because you should focus a lot of attention on foreplay, I suggest that your play with each other fully clothed for the first thirty minutes of the appointment. Choose a lady that cares about personal hygiene and present yourself properly bathed and well groomed (hair, nails, breath). Be a gentleman at all times.
You are young and unless something is wrong with you, you are going to pop several times during the two hours. Choose a lady that will accomodate you.
If you focus on choosing a lady that turn you on, on good foreplay, on being well groomed and being a gentleman at all times, the session should be one that you will remember in a positive sense years from now.

Good advice all around