HIMu is the best, beautiful otherworldly design. That panel where he's looming over the trees having defeated Loki is gorgeous. Really looks like a proper final villain.
Primal Luffy looks good but I want to see more of it before putting it above my goat Boundman. It is promising though and already miles above Vanilla G5.
Loki looks good to me, but I agree with most that it wasn't as cool as it could have been.
To be honest I really like the weird vibe it gives off more than anything else, it's a kind of "fascinatingly ugly" design. Imo the face is the worst part, needs to look less like X-Drake amd more like a Viking helm.
With all that said I hope the hybrid that he used in his flashback is better and stronger. Sad that this one got jobbed.