Hi,I have not tried either for this niche, but I think both methods would work well if you do it right. I would go along with Facebook first though as a result of tens of millions of people move through it daily so there’s the high amount of traffic which you can tap into. But before going into Facebook, I suggest you place up a page in your site/brand and share significant content material, boost posts, etc. You might want to have a look at too. It has spectacular pointers on what content material to create for your site which that you can share on Facebook.
The good thing with social media is you get to engage together with your audience, and here’s important in niches akin to the fitness niche. Like minded people, or those that are facing a specific program losing weight, getting over a sickness, etc tend to look for support groups where they can share their adventure and gain more advantage, or at the very least, find moral aid. So you’ll find fitness associated groups in Facebook. You can take part and jump into the dialog, share useful insights. You’re not just getting traffic here, you’re building online presence to your site.
Hope that helps.