The Eclipse is a studio multi-fx tool that can also be used by guitarists. The Axe is a dedicated guitar processor.
Eventide make truly fantastic stuff, I use the bigger model H8000FW in our studio. But the Eclipse is NOT a tool designed primarily for guitarists. I'll quote Eventide's own website - "Whether it’s live performance, front-of-house engineering, or quality studio processing, Eclipse gives you the tools you can depend on in one compact, professional package." In other words, you'll be paying for a lot of stuff you'll never use, and you'll get frustrated because it's internal routing is far more geared to what a recording engineer would want, rather than a guitarist.
The Axe however is a tool designed from the ground up for guitarists. As someone who owns both Eventide AND Fractal products, I strongly recommend you go with the Axe. You'll be much happier with it.