You can't really go wrong when choosing a guinea pig. They all have very similar temperaments and requirements. Many owners set out with a particular GP in mind, in terms of coat type and color, but on the way they fall in love with a different type of guinea pig, and that's that.
The main question is this: How long do you want to spend grooming? If the answer is not long at all, then you’re best off opting for a short-haired breed. If you like the idea of handling and combing a long-haired breed, just make sure you actually have the time to do this on a regular basis.
Some breeds of guinea pig have long hair, such as this Merino
Guinea pigs are relatively recent pets, and unlike dogs and cats the species has not had long enough to be bred into radically different types or temperaments. So there’s no real difference in personality between the different breeds. All you need to do is pick one that looks good to you - and that's pretty much all of them, as far as we're concerned!