Here’s what my friend wrote (copypasted, any dumb spelling mistakes are his) - keep in mind he’s primarily a guitarist who dabbles in synths:
Depends on what u want to do with them, I guess. HX is more flexible, H9 does way cooler shit. HX can have multiple effects going at once but some of the H9 algos are multieffects but it can only have one going at a time, why I have two of them. H9 verbs sound WAY better, and I think their delay is nicer. Actually most of the H9 effects sound better. It also does lots of weird stuff like their cool plugins Hotsawz, Blackhole, Crystal, mangleverb, Harpeggiator are all way out and super fun. HX doesn’t do anything like them, but it does all the standard effects stuff all at once and is easier to use. HX Looper is dope and one of the best I’ve ever used on the floor. HX has better distortions, but it still blows for anything other than rock or just fattening stuff up. I stick to analog pedals for disto.
HX is better playing live and it’s easier to control on the fly. H9 feels more like studio gear in a box, but they hold up live if you get everything dialed in before. H9 is better for me on synths, HX feels more like guitar effects if that matters. The Eventide mostly sounds better to my ear but the HX is totally solid, especially when your rocking out full volume.