Gentle- A Beta Reader who will spend a lot of time working with an author, and who will really spend time making sure an author gets it right.
Flexible- A Beta Reader who is flexible is more likely to send a chapter back multiple times, and is usually willing to work with you no matter what your needs. Flexible Betas are usually willing send a chapter back and forth multiple times to work through a problem.
Brutally Honest- This type of Beta does not sugar coat anything. They will tell you exactly what they think, while remaining helpful and encouraging.
Essentials Only- Strictly the necessities. Grammar, Spelling, Canon, Characterization, and Plot. Useful if you are on a deadline.
Comprehensive Critique- This style focuses on all the necessities, as well as critiquing your work. Useful for newer authors, or really anyone who would like some style advice.