I did most of LEEWS (never finished the last CD). I found it useless. IIRC, it's basically RAC (IRAC minus the issue statement). My school, though, had an "intro to law" one-week course before regular classes, and we learned the basics of how to synthesize cases, outline, and take an exam. The only useful thing I got from LEEWS was that you don't need to state the issue explicitly; I usually just used headings/subheadings to key the prof into what topic I addressed. But I also had one prof who specifically said "use IRAC, including the issue statement." One of my other profs wanted CRA (conclusion, rule explanation, rule application).
I thought GTM was a much better use of my time. It's more abstract and less of a "process," but it really helped me understand what professors are looking for in an exam answer (rather than how to structure an exam answer in a format that not all professors necessarily like--LEEWS). I also read GTM before LEEWS, so maybe that's why I thought all the fork-like discussion (who's against who, and what argument can they use) in LEEWS was not very helpful. Maybe it's helpful if you didn't read GTM.
I did LEEWS before GTM. And aside the Czars of the Universe chapter I thought LEEWS was better. I think this, like a lot of things, depends on the situation. My school had barely any direction the first week beyond such things as diversity training, personality tests, and the regular orientation stuff. Also I think it depends on the person, what you already know, and how good at test taking you are. A lot of folks in my school did LEEWS to some level of success. The true test will be when grades come out. But overall I think it was worth it. Although I must say Wentworth drags that thing out into 9 hours of droning when he could probably do it in like 4 or 5.