Which workout plan should I start with?

This is probably a stupid question but I really want to get into a fitness routine and I’m having trouble deciding which plan I want to start with. Back in the day I purchased two different e-books from two different “fitness stars” and haven’t tried either of them. I’m finally in a place in my life where I have time to devote to getting stronger/more in shape, but I can’t decide which to start with (my goal is to have completed both someday!)

The 8 week plan is the “sweat it to shred it” ebook by Sarah Stevenson, also known as “Sarah’s day”. It doesn’t necessarily seemed designed for beginners or advanced, but I do think having a shorter goal might be more motivating.

The 2 consecutive 12 week plans are the BBG guides by Kayla Itsines. There is a beginner add on plan that’s 4 weeks that I can also do before I do the 2 12 week plans.

Has anyone done both/either of these plans and have an idea of which is better to start with? For the record I’m not totally out of shape — I’ve run a marathon in the past year and I’m about to run a half in three weeks. I also had a labor intensive job where I hiked a lot of stuff on my back up a mountain a few times a week this summer/fall.

Thanks for your help!!