Do a search on this subject. It has been discussed many many times. Everyone has their favorite wax that they prefer to use and all of them do a good job. Just go with a well known name brand and you should be happy. As a pro detailer, I've tried many brands of waxes and have not been dissatisfied with any one brand.
To answer your question regarding wax for dark colored cars, Meguiars Gold Class is one that I don't prefer using on dark colored cars. It's a very good wax but the areas where the wax goes on thicker, you'll see darker lines after wax removal. You'll just have to go over the area several times until they disappear. It's a great wax but just takes a lot more elbow grease to remove all of it especially on dark colored cars.