Welcome to AviationStackExchange. The question that you asked is definitely not a question that solicits fact based answers. Something that is usually frowned upon on this question and answer forum. Hence the down-votes and close-votes from others. My answer (as well as any answer to this question) will be very biased and opinion based.
In answering this question, I would like to separate your time spent on ground school into two categories. Those are:
- Ground school in preparation for the knowledge exam / written test.
- Ground school in conjunction with flight training.
If you are preparing for the written test, online ground schools are a great supplement to the FAA provided materials. All of the knowledge exam questions are taken directly from or have a reference to either an FAA official Handbook, Manual, Advisory Circular or other publication. Each publication and subsequently each question is written by government officials with the review of government attorneys. They can be very dry and sometimes hard to understand. Most of these publications can be downloaded for free from the FAA website.
Many online ground schools will teach these subjects in a way that is more easily understood and palatable than studying on your own. Plus, you can immerse yourself in aviation by replaying the lessons while doing other activities like driving or cleaning the house. Studying the lesson with total concentration, then replaying the lesson throughout the day will help the material sink in. Many also have free tutorial YouTube videos and podcasts to help with that immersion. My recommendations for that are:
- King School
- M0A or MZeroA
- The Finer Points
- Aviation 101
- Rod Machado
- Aviation Training Network
- Bold Method
Ground school training in conjunction with flight training is another story. You will sometimes hear the old aviation trope/saying, “The cockpit is a horrible classroom.” It is very hard to learn the academics of flight in the cockpit. It is even harder to absorb the material while dealing with the stress of flying. Investing the time and considerable amount of money to learn face-to-face with an actual instructor in real time is invaluable. It is also more effective and cheaper than trying to do the same while paying for a running aircraft engine.
Each flight should begin and end with a ground school lesson. Even a short one. At the very least, a detailed briefing and a debriefing should be done. You will find it more advantageous to do those sitting comfortably in a building rather than in a cramped cockpit on a noisy ramp. Some subjects like weather, physiology, Aeronautical Decision Making, flight planning, etc. are best taught in a classroom setting on the ground. Some ground school lesson will be so intensive that they will need to be done on separate days from your flights. Don’t shy away from nor neglect to take advantage of this investment. It will save you time and money in the long run. Plus, you can log that time in your logbook as proof that some type of ground instruction was done for certifications, ratings, endorsements, flight reviews, etc.
My recommendation would be to first get your medical exam done if it is required for your ultimate desired pilot certificate goal. Next, find and interview many different flight schools and CFIs to find one most conducive to your schedule and personality. Go for a Discovery Flight to see if this activity and instructor are the right one for you. Then, ask the instructor with which online ground schools they are most familiar. Use that ground school to prepare for the knowledge exam. That way you can discuss with them and ask questions regarding specifics from the lessons. Procure sample knowledge exams to study in detail. The FAA are notorious for the way they structure their questions and answers. I would recommend exam study programs like:
- Flight Test 5 from Sheppard Air, Inc.
- Study Buddy from Sporty’s Pilot Shop
- Prepware from ASA (Aviation Supplies & Academics, Inc.)
Then, take and pass all of the knowledge exams up to the level of pilot certificate you would like to achieve before starting the rest of your flight training. It is totally possible to do well on these exams without ever having set foot in an airplane. And, it will prepare you well to be a student pilot before your flight training. It’s also a weight off of your shoulders to have one less thing to worry about during your training.
*Disclaimer: The views, recommendations and opinions of this poster do not reflect those of AviationStackExchange.com. 😁