Just to share my GMAT experience on verbal as well since there was a question posed earlier on achieving a high verbal scores. I have used only Kaplan and OG.
I found Kaplan's RC really difficult and was pretty discouraged after doing them. Because I was doing so badly on Kaplan RC, I tried Kaplan's suggested approach of jotting down main points of each para to get a good overall view but I found that that took too much time and generally didn't give substantially higher payoffs. I found note-taking useful only for those scientific passages with lots of unfamiliar terms. The RC on the real test were much shorter and easier to understand. Didn't have to take down any notes at all.
I think working hard for SC gives the highest "ROI" as there are rules (e.g. idioms) one can learn.
On CR, I wasn't initially good with the "bold-faced" sort of questions, but practising and re-doing those questions in the OG will help you to understand what the question is really asking.
I wasn't expecting a high score for verbal at all, so it might very well be a fluke! Though the day before the test, I also managed to obtain a pretty good verbal score for a GMATPrep tests. But I reckon that it was because I had done the GMATPrep test before.
Well, I wished I had learnt of this forum earlier! Would have picked up valuable tips to help my quant scores.