We do not currently have a poll for such a thing, but there is something about tests:
https://www.beatthegmat.com/best-practic ... t1327.html
I don't know if anyone here can provide a detailed reasoning on why a test prep company is better than the other for the simple reason that most people can't afford to buy more than one package.
You do have a lot to choose from and it's probably ultimately up to you if you pick one company over the other:
- Veritas
- Kaplan
- Manhattan
- Knewton - I've actually participated in a few sessions for this one and found their teaching method quite good, but bear in mind I have nothing else to compare them with