1. Use descriptive titles to your threads please. "Please help" doesn't tells anyone anything, especially because this is already in the help forums.
2. I average around 12, 15, and 19 for ZZ, CFOP, and Roux. I have never mained Roux, and only mained CFOP for about 7-8 months before switching to ZZ about two years ago.
3. CFOP will probably get you sub 30 faster because you already use beginners. The transition from corner->edge to corner+edge (F2L) will take a bit but since the other steps will remain largely unchanged, you should adjust fairly quickly. I would suggest figuring out F2L intuitively. After you have solutions for all ~40 cases, comparing them to algs from both expert cubers and just from algdb. This way you'll have the fundamental understanding of F2L, but also eliminate all of the stupid beginner mistakes and get good algs.
If you use Roux, you might lose the race to sub 30, but you'll probably win the eventual race to sub 20 and so on. Because Roux has a fundamentally different approach, it will take longer to learn, since you will be relearning more. If you do chose roux, try and refrain from using CFOP-y tricks to solve blocks. Learn proper block building and L6E techniques and finger tricks.
However, all of this is purely affected by how much you practice. If you only do an average of 12 a week, you most certainly won't get sub 30, no matter which method you chose. If you do 100 solves a day, you could get sub 30 even without changing from beginners.
tldr; It really doesn't matter. Pick a method and start doing solves