Nuke: Excellent package, Shake is being, or been discontinued by Apple, so it might be worth while holding off, although Shake is an awesome package.
Fusion: There is a lot of places use Fusion, like any other package. Once you get looking for them, you will find them. www.vfxtalk.com have a look in the “Job Lot” part of the forum, as there is always comping jobs using various packages being placed in there.
Making your decision is purely your choice. What ever package you choose there will always be work for it. I suggest downloading the trails for them all, and see which package suits your paticular workflow.
I for one am looking into the Fusion course’s this term over at fxphd.
I hope this helps a little.