As you might see if you check the latest commit on the linked github repositories, ninja's version is not being updated, while otx is being constantly updated (which people consider as cluttering with unnecessary features).
Basically otx will have more features but is arguably full of useless stuff (according to people, I do not say this is true or not). I have made no comparisons myself and have no insight in the contents of either, so you might try to use the search feature to read about either of those versions and make your own opinion.