I have taken the Kaplan and Princeton courses and I used to teach for Veritas, but I will try to be as unbiased as possible.
Kaplan and Princeton review give you less hours and make you take supervised practise exams (on your dime -- you pay for the time). Veritas has the most hours per class (42) and you take exams on your own time.
Veritas requires that their instructors all score above 750 (99+%) on the GMAT and we must prove it. Kaplan require 95% and Princeton review only 90.
Veritas is a new company and their material and training techniques are in flux. The support materials are not as mature or complete as those of the big 2. However, they hire VERY good instructors (I have met many of them at our training conference), pay them well (to attract good talent) and give them considerable freedom to apply their own techniques. Veritas de-emphasizes "tricks" and does a good job of teaching solid principles, teaching solution strategies by question type. There is a LOT of homework. Princeton Review and Kaplan have tons of experience in test training, but I felt as though the techniques were "tricky". The Kaplan and Princeton review books and materials, however, IMO are very good and well organized, especially the Math and Quant workshops. However, you can buy the books for $20 anywhere. I will honestly admit that I use their stuff to teach fundamentals and supplement my own materials (why reinvent the wheel?) IMO, PR and Kaplan are interchangeable, but I would pick Veritas every time.
I currently teach for
Manhattan GMAT, based in New York, but recently expanded to a few major cities like Chicago, Boston, San Francisco, Los Angeles/OrangeCounty/SanDiego. I live and teach in Southern California. In my opinion,
we are the best and I jumped ship because I really believe in the company, even though I really enjoyed working for Veritas and my students were all very satisfied. In addition, Marcus and Chad, the owners, are great guys and are very accomodating to their students as they try to grow their business. Like Veritas,
Manhattan GMAT only hires instructors with 99%+ scores and
significant teaching experience. The priority to teach students and classes, however, is in no small part determined by our student reviews, which tends to weed out the more ineffective teachers. The materials are top-notch, and I actually learned a few new techniques that I have adopted over my own (something that did not happen at the other three).
If you live in on of the major American cities, or you can afford private tutoring done via the internet and phone, I
highly recommend
Manhattan GMAT. (I spend a fair amount of time here so you can browse through my postings to get some idea of the quality of my teaching. All of my peers are as good, or better!).
However, Veritas, Kaplan, and Princeton review have MUCH more geographical coverage, and of those I highly recommend Veritas.