Personal Opinion: Dark Harvest is the most fun rune in the game.
With DH's overwhelming prevalence in the pre-season, despite the recent hotfix, I wanted to offer my 2 cents on the whole affair. I think that Dark Harvest is simply the most fun rune in the game at present. I feel like it's one of the most simple and straightforward runes in the game currently and I think that's part of its appeal. It's extremely effective at facilitating one of the most enjoyable gameplay elements within League: Harvesting the lives of enemy champions. The stacking mechanic is super fun and does a great job at incentivizing you to hunt for aggressive plays. I think this rune has a lot of parallels with Flash in the early days of League. In the early days, the consensus on flash's power isn't what it is now but most people I met agreed it was the most fun option to play with. I feel like Dark Harvest is in a similar place and I kinda hope it gets treated similarly. It'd be really unfortunate if this fun option is no longer viable/strong due to it's popularity.