Selected answers from the Dumb SEO Questions Facebook & G+ community.
Jacob Punton: Keyword planner, but you need an ad campaign running to get exact data and metrics
Alan Bleiweiss: Moz Keyword Explorer is, in my experience, more helpful, though to be fair, I use Keyword Planner for rough estimates to get clients going.
What do you do to see which keywords are easy to rank for or not. What tools, what methods, metrics etc.. 
