I don't have any that I specifically use, I just hunt down the ones which will give a positive ROI when I purchase the upvotes. :) It's pretty easy on steembottracker.com, where you can check the the current total of bids and value of the bot's vote. As long as the bids are lower, you'll at least break even. There's usually a suggested max upvote which makes it even easier too, takes out a lot of the math.