I started with just the official GMAC materials, but I quickly realized that theirs was not designed to help you "crack the code." I did quite a bit of research and was completely willing to pay for the in-person or online classes, but I didn't want to be hamstrung by the pace of others. I opted for the Kaplan self-paced and I'm very glad that I did.
For me, my work schedule was at a lull for a couple of months, so I decided to just hit it as hard as I could. Because I was doing the self-paced, I was able to do 8-12 hours of study per day. The intro video was oddly super helpful. It told me how to organize my studies (don't take another CAT unless you've done significant studying, etc.). I mapped out a plan for myself and got to it. I started with a CAT and then the program told me where I was and what I needed to study more of. I was in a position to skip all the basics and I jumped right in to the intermediate and then moved on to the advanced.
I will say that the Kaplan CATs aren't perfect representations of the actual GMAT, but they're close and they're included. I purchased the GMAC test expansion pack and I budgeted them out so as not to burn them before I got my target score.
Once I had done enough Kaplan studying that the Kaplan CAT said I was getting into the ballpark of where I wanted, I took the GMAC official CAT. It said I got a 760, so I scheduled the official test for two days later, took a day off and took the test. I only got a 710--good, but not my target. In hindsight, my concentration/stamina waned towards the end of the test. Gratefully, the GMAT now allows you to choose the order to take the test. I recommend doing your weakest (verbal/quant) first, the other second, and doing the IR/AWA last since those don't figure as prominently into the admission decision.
I continued with the studying, reviewing carefully and dissecting advanced problems until I could "see the matrix." About 6 weeks of total studying, and I got a 740, still shy of my target of 750, but it wasn't worth it to keep studying to get another 10 points.
My favorite part of the self-paced was that I could watch the videos at 1.5 and 2x speeds until I found something that met my personal needs, then I would pause and write it down and rewind/re-watch as necessary. At no point did I feel like I was missing out on quality instruction just because the instruction was taped. On the contrary, I actually think the instruction was better than I might have received in an online live class, because the instructors were clearly some of Kaplan's absolute best.
A few times I had questions about a review or example question and I emailed Kaplan. I received answers usually within a business day and was mostly satisfied with the response that I got.
I absolutely recommend the Kaplan self-paced course. Especially for those whose skills are already on the intermediate-advanced level and who are trying to figure out how to go from ~80th percentile into the 95th or better. You can just keep hitting the parts that trip you up until you get there.
Also, I didn't use it, but it does come with the official test day experience. I'm a good tester and had already been to this location, so I didn't want to waste the time practicing, but for some, I could see how helpful it could be.