I used multiple beta readers on my book (mystery/suspense), four to begin and then a fifth asked if they could do it as well. For all, I sent the entire thing, with some specific questions (plot OK?, characters well drawn, enough clues to make ending make sense? I asked each to give me feedback within 6 weeks, no matter how far they had gotten, and again when they finished the book. As mrsmig said, I looked for areas of agreement among all of them and used them as the main guide to revising the manuscript, but I also incorporated individual comments re how some of the characters interacted into my revision as well. I think getting multiple betas when you are working on your first book helps as you are getting more opinions and should help you build something that will sell nicely. If you should be fortunate enough to write multiple books, you may be able to narrow down your beta readers to those that provide the strongest and most helpful reviews for that type of story.