What is the best online dating site for a woman in her 60s?

My vivacious and beautiful mother-in-law, who is 67 and was widowed long ago, has agreed to let me post a personals ad for her in the hope of finding a companion, maybe more. Any ideas about what sites might be good ones for her? She lives in the Portland, Oregon metro area (I mention this in case there are differences regionally). Thanks!