Im a pest control guy. For baiting rats I have found Nutella to be very good, sunflower seed butter is much more attractive than peanut butter, and for those very tough to get rats Silvas Hot Linguisa. The trick is to never use very much, just a smidge in a trap, a little more than a smidge on a plate or open surface. If you can, tie it down or secure it in such fashion as they have to work at it for a bit. Having said that, the absolute best bait is what they are already eating, if its nuts, use nuts, if its fish use fish etc. So before any "control" measures are taken its vital to do some reconnaissance to find out as much as you can about their food, avenues, exits and hiding places. Having done all that, you have the upper hand and will likely not fail. I don't want to come off as a know it all, but with 35 years in the biz, if I don't share what I know with anyone interested it doesn't amount to much. Good luck.