Honestly this is a question with no clean answer, but I'll share what actually moved the needle for me.
I prepped for the GMAT Focus Edition and landed 725. I tried a few things before finding what worked, so hopefully this saves you some time.
For Quantitative, the single best thing I did was not buy a course at all -- I used the Official Guide questions religiously, but more importantly I started keeping an
error log. Every wrong answer, I'd write down the exact type of error I made (conceptual gap, calculation slip, misread, time pressure). After 3 weeks of that, patterns emerged. I was terrible at Work and Rate problems. Knowing that, I drilled specifically on those rather than doing random practice.
For Data Insights, this is the section that I think matters most right now because it's new and most prep materials are still catching up. The Two-Part Analysis questions in particular are under-covered in most courses. I'd recommend spending deliberate time on DI -- it's genuinely scoreable if you approach it systematically.
For Verbal, Critical Reasoning was where I improved most with structured prep. The key was learning to identify argument structure before evaluating answer choices. Rushing into answer choices without understanding what the argument is actually claiming is the #1 reason people miss CR questions.
What didn't work for me: video-heavy courses where I was passively watching explanations. That felt productive but wasn't. Active problem-solving with immediate review beats passive consumption every time.
The "which course" question matters less than how you study. An hour of focused, reviewed practice beats three hours of going through motions.