Hey master, boy that's a loaded question on this forum. I don't recall where that topic offhand was debated but it always comes down to personal preference.
There are those that are King video camp, the Sporty's etc and you also have the Gliem ASA and Jepp books.
Here's my personal preference: I use ALL of them actually! The King series has cornball humor but covers the subject matter well. They focus more on the test questions and answers and some practical advice I guess you would call it. The Sportys is drier and more straight forward like ground school but doesn't quite delve into the questions and answers as much. The thing is I think where one of them focuses and the other doesn't is why I use both to give me more info and a better rounded study.
I use the Gliem and use the Jepp.Don't forget about the Far/Aim also and there you also have different company's that put that out also. Most of the time I have used the Jepp Far/Aim and liked it just fine but yesterday I was refering to Aviation Weeks publication and it was aranged differently and I had a hard time finding the info I wanted because it "seemed" all mixed up. Hard to say, I was probably used to the Jepp.
So I hope this helped somewhat, but will see that it really depends on how you assimilate the info you get from whoever.
I like the Gleim manuals because they are outline form and are really cheap. Their practical test prep does a good job going through the PTS and explaining each step. I also like the Jepp manuals because of the pretty pictures
and the format is well thought out. ASA makes some pretty good stuff too with their manuals by Trevor Thom, PTS guides, and Oral exam prep. I've used them all and can't pick a favorite. I plan to use the King cd-rom course for my CFI and FOI test prep. I have the course already and it seems like it will be very beneficial. They are all good study materials and each one has its pros and cons.
I used Rod along with Jepp and ASA for my private. While I appreciate his humor his books are really long. He really dumbs things down and explains them in a comprehensible manner but it is not in a concise format.
I really enjoyed both Rod Machado's private pilot handbook and his instrument flying book. There is a ton of info in the Private book but there are many color illustartions and jokes in the margins that make it easier to get through.
Besides that, the FAR/AIM is really your best study resource, as is any other official FAA publication relevant to what you're doing. I use the FAA's Pilot's handbook of Aeronautical Knowledge and the Airplane Flying Handbooks qutie often.
I also study the POH of my aircraft reguarly just for safety purposes and for oral/practical exams, I do my best to know everything in the ASA Oral Exam guides and the PTS. For writtens, Gleim has given me the best results (never scored less than a 98 when using gleim to prepare).
I prefer material that comes straight from the FAA because you can be pretty confident that you're learning things you need to know for your practical if it's in those publications. However, for ab initio type studying, a resource like Rod Machado is better because it puts things into plain language.
I went through the Cessna CD's and IMHO they didn't do a really good job of prep'ing me for the written. I actually went out and bought the Gleim book after I finished all the CD's.
The Cessna program just seemed to gloss over things...weather esspecially. On top of that They never really show you what the FAA exam is going to look like. The Gleim book uses actual questions from the exam, but not only that they really give clear consice and thorough explanations of the answers.
I know more now after going through 5 chapters of the Gleim book than I did after 21 Cessna CD's.
I'm studying for my CFI so I would reccomend anything and everything from the FAA. If I could do it all over again, I would use Jepp for PPL. It was good for me and has lots of pictures and puts things into english. Then go to the FAA for instrument and comm (I used Jepp). The material is the same, but not as pretty if you use the government publications. If you plan on getting your CFI I would just suck it up and use the FAA books as my main study resources and then go with others to supplement. If I'm stumped on my checkride and I have to look something up, you can bet I'm going to dig in the FAA books first!
As far as writtens go, I've used all Gleim and had pretty good success. I think my lowest score was a 93% on my instrument written.
I like the Aviation Publishers books, it's a Canadian company and it emphasize flying in Canada. Their most succesful book is without a doubt From The Ground Up, it's litteraly a pilot's bible for the PPL and CPL theory.
Then I also use one of their books called Flight Test Note which helped me alot prepare for my PPL flight test, again it can be used for the CPL also.