I have an island that does not have a sink, as I wanted a large flat surface. If I had it to do over again, I would have put a small prep sink with garbage disposal in the island -- if it could be on a different side of the island from the main sink and work triangle. That would have allowed a second person to prep veggies for me without getting in my way as I cook. I would have done the sink in such a way that I could place a cut-to-fit wooden board on top of the sink to create a flat surface all-over. The wooden board could double as a cutting board too.
If you are putting in only one sink, then I would like Kathy T's setup as long as the sink and dishwasher are out of the path of the refrigerator and stove.