This has been a dilemma for a long time. I personally don't like ads at all but had to do it to sustain. That's why I'm building alternative streams of revenue so when they become big, I can remove ads altogether.
I would set a goal on where/when you decide to remove ads... It's really easy to keep that extra revenue as it will tend to grow with your site. Beyond this, having the paid subscribers get an ad-free UX when logged in?