Hey,
I'm no expert, and I haven't even written the exam yet, but I was in the same position as you when I started preparing.
I scored Quant 25 in my first practice test or something ridiculous like that, so I definitely understand how you feel about Quant. I haven't yet taken the exam (it's in less than a week) so take whatever I say with a grain of salt, but this is how I've been preparing for it.
My fundamentals were terrible. I didn't know how to approach a simple Word Problem or a Geometry question. The Manhattan Strategy guides really helped build my foundations in Math. I started with Algebra and worked through all the guides 1 by 1. The 1st time I skipped all the "Extra" and "Advanced" chapters and just did all the practice questions at the end of each session. I also did the corresponding "Easy" and "Medium" sets, with about 50-60% accuracy on the Medium ones. Once I finished that, I practice mixed problems on
Magoosh, and eventually went back to the Strategy guides to work on the advanced sections and the "Hard" question sets. Manhattan definitely made my fundamentals extremely strong, from then I would atleast have an idea on how to tackle each problem, even if I didn't get it completely right, atleast my thinking was in the right direction.
Once the guides and all the question sets were done, I started doing mixed practice on
Magoosh. The answer explanations and videos really teach you a lot of tips and tricks on how to tackle even the hardest questions. With this, I managed to score Q48 in my 1st CAT and Q49 in my second. I've been working on the GMAT Club practice tests since my first CAT.
This is just what worked for me, because Manhattan made me learn my concepts by doing "Non-GMAT" problems before I moved on to tackle actual GMAT ones. I also prefer learning by doing, so I found this to be extremely useful. If you are looking for a resource for Quant, pick up one of the books and give it a whirl. If you like it, you can always buy the others, if you don't you atleast get 6 free CATs to use!
Again, I'm no expert, and I haven't even written the exam yet, this is just based on my experience. Feel free to contact me if you need to know anything specific!
Good luck!