As a lot of the posts mention above, it depends on what kind of a learner you are. For the writtens, I recommend going alone with the Gliem. Besides saving you $$, you can study at your own pace. All the questions and answers are in those red books. Couple the books with the written exam CD's and you've got it made. With the CD's you can create your own tests. This helped me a lot.
To obtain my CFI/II tickets I went to American Flyers. Thru them I did the weekend written courses (CFI-A, II and FOI) and they were horrible. They were extremely uninformative and unorganized. This was proven when people in my class were failing the writtens. After witnessing this I went out and bought the red books, and after I felt I was ready I took the writtens.
As for aircraft systems, weather and flight planning, your CFI is probably the best route to go for learning.
To obtain my CFI/II tickets I went to American Flyers. Thru them I did the weekend written courses (CFI-A, II and FOI) and they were horrible. They were extremely uninformative and unorganized. This was proven when people in my class were failing the writtens. After witnessing this I went out and bought the red books, and after I felt I was ready I took the writtens.
As for aircraft systems, weather and flight planning, your CFI is probably the best route to go for learning.