Paint, Keyer, Color correction, motion tracking and stabilisation, and RPF support (with channels and 3d post effect, including UV retexturing) are far superior in Combustion.
It’s also, to a point, node based, has proper motion curves and can save complex effect pipelines as capsules to be reloaded and reused later.
Plus it’s always been working natively to support float depth in bitmaps.
It has its own drawbacks and bugs, but it’s not like AE hasn’t.
I haven’t tried 7.0 with the “new” (for them, of course) 32bpc support (or float, if you prefer) and motion curves.
Most plugins that work in AE do work nicely in combustion, provided you give them the same type of footage (ie. most won’t work in float depth).
It ain’t a “photoshop based” app, though, so the workflow is fairly different to AE, and more akin to Flame/Inferno (with shared LUT tables and Keyer technologies).
I’d suggest you to try the demo to you heart’s satisfaction, and only then try and make the switch if you feel like.
Fusion’s extremely cool too, with very good reasons to adopt it (incredible variety of file formats readable and writable, very nice toolset, full 3d particles, very good keyers and CCs, and on and on), but if combustion looks like a stretch from AE, fusion is lightyears apart.
It all boils down to what you do with your footage, and how best you like to work 
Have fun choosing!
Lele