Number one priority for me is the quality of the writing, followed a close second by the subject matter. I try to follow hubbers who match the criteria and who share a love of certain topics - poetry, drama, nature, travel and sport in particular. I tend not to follow those who overcook the personal when they write.
Why quality of writing first? Well, really good writing can turn the most obscure subject into a must read and is in itself a pleasure to digest, like good food. I tend to wince when I see spelling and grammar mistakes, they totally put me off.