I like the burger at Paulies in Saugatuck. Their onion rings are awesome with it too, but they can take a little more time than usual to make it on account of their small kitchen. Great Patio on a nice day too!
There is a little hole in the wall bar in downtown Davison called the Davison House. Used to be called the Davison Hotel but was just recently sold. The new owners have some of the best burgers I've tasted. If you get a chance, stop by and check them out.