I had been subscribed to Wanikani for at least half a year, iKnow for a month, and after reading this post, I signed up for a free trial of Cooori, and out of the three, I definitely like it the best thus far.

At first I liked Wanikani due to it's creative mnemonics, but I hated having to learn radicals, kanji, and vocabulary separately, having to reach a certain proficiency in each category before unlocking the next items. The way it forces the learner to slow down is irritating to say the least, and makes it more profitable for them. I will give it points in the forum department though, a very active and interesting community. In the end I decided it wasn't worth the money.

I took a break from serious vocab study for a while, trying to do Anki again for the umpteenth time, but still having a rather meager vocabulary, it wasn't worth it for me at this point. Then I decided to try out iKnow. It was a substantial improvement over Wanikani for me. I liked being able to work at my own pace, and the example sentences to help reinforce words, but I felt like the example sentences were too simple. I was looking for something with a little more variety in the grammar department.

Finally, after looking over this thread, I checked out Cooori, having never heard of it before. So far I really enjoy the diversity in the sentences. The vocab seems to build cumulatively too, which again, helps reinforce knowledge and forge links between words. I'll definitely be subscribing for at least a month (if not more).

In the end, if you're only considering between iKnow.jp or Wanikani, go with iKnow. Wanikani is frankly a waste of time and money. There's plenty of other active Japanese forums elsewhere.