Yeah that't the thing - what qualifies as "great" is going to be different for everybody. Personally I found some by looking at the New, Trending, and Hot lists, but those are very hit and miss. Scouring posts with particular tags of interest helped too. Then from the ones I did like and follow, their resteems helped a lot more, as well browsing the lists of who some of them follow, plus seeing the occasional good commenter who stands out. It's a slow process though and tends to keep your feed very niche, with little chance of being exposed to something truly new unless you purposefully go looking for it.