The best course is the one that gives you enough depth, structure, and practice to actually get you from your current level to your target score.
If you are building your GMAT skills from the ground up, I would strongly favor a comprehensive course over trying to piece together your preparation from videos, Official Guide questions, and random practice sets.
A good course should:
Teach Quant, Verbal, and DI comprehensively
Build concepts and skills in a logical sequence
Give you substantial topic-by-topic practice, not just a handful of questions in each area
Teach strategies and test-taking skills in addition to content
Track your weaknesses and tell you what to work on next
Provide detailed explanations when you get questions wrong
Give you enough practice to turn knowledge into reliable performance under time pressure
Official GMAT materials can certainly play a role later in your preparation, particularly the official practice exams, but they do not provide the depth of instruction or volume of topic-specific practice that many students need to build their skills.
Of course, I’m biased, but I would encourage you to take a look at
Target Test Prep. We designed TTP as a comprehensive GMAT preparation system covering Quant, Verbal, and DI, with a structured study plan and extensive targeted practice.
Whatever you choose, take advantage of trials before committing. Actually work through some lessons and questions rather than just comparing marketing pages.
If you post your current score, target score, and how much time you have to prepare, we can probably give you much more specific advice.
Good luck!
Scott
Target Test Prep