My default is to mash a high gear, and spin a lower one for hills and headwinds. I do tend to use a higher gear than most for hills, and do a lot of standing.

Lots of threads about this--people need to use whatever works best for them and ignore people who try to prescribe the superior method based on what works for them. Legs and cardiovascular systems are not standard issue, so different styles suit different people.

And there really is no evidence other than anecdote (not scientific) that mashing is bad for the knees, but expect a bunch of posts that will state that as fact. It appears to be an article of faith amongst trainers, but I've never had anyone successfully produce a study of any kind that indicates that this is so.