Planning to run few ads,Need help!

My campaign is to sell weight loss diet plan.
My site is up now and I am slowly working on seo myself.
However since the niche is just a diet plan and not physical product I am planning to run few ads to see if it works for sales.
I am a bit confused with what to try first? I have two options for now,1 Adwords, 2 Facebook ads.
I am going to manage my budget is such a way so I can give try to adwords,fb and bing of course.
I'd like to get suggestion from you guys what should I start first? Please choose your option below and mention a small logical reason why you believe that advertiser is fair for first try.

1. Facebook
2. Adwords
3. Bing

Sorry if this is wrong section I cannot understand where to post it.

1) adwords - new accounts can use a get $100 when you spend $25 coupon
2) bing ads - new accounts get $100 coupon (make sure to find the coupon code first before opening the account, same with above too)
3) fb ads - no coupons I know of

It's hard to say. You'd probably get the best results from Facebook, but their terms are strict.

Make sure you read them all over and be careful not to break any.

Facebook ads are nice because you can target specific people versus targeting keywords with Bing or Google ads.

Facebook ads are what I would recommend to anyone. I would advise you to pick up some good Facebook courses so that you know how to target properly. I'm no expert but from observing others, it takes time + practice to target a specific audience that will bring positive ROI.

I agree Facebook allows very precise targeting. If you have ANY idea who your target customers are I'd use Facebook.

since it is direct B2C you could go for FB target women specific and men specific campaigns

Take your time OP, read the following sections:
http://www.blackhatworld.com/blackhat-seo/f13-pay-per-click/
http://www.blackhatworld.com/blackhat-seo/f175-media-buying/

Sign up to all platforms and start exploring. Don't start a campaign until you feel comfortable and test everything. Read up on split testing(A/B testing) and when you have some experience then retargeting.