I use them more, but I use Google on a certain browser. The good news is that Google doesn't track me since i use scr....e. And it's also encrypted and with zero ads. With Google is creepy since you are logged on maybe to check adsense, gmail, blogger or whatever so they know the exact name of the person that searched for a certain question.
SEO wise, I don't really know much since I haven't changed them for Google or Bing. I know that Bing, so far, does not use unproven and radical signals that cause your traffic to crash by 70% overnight.