Welcome to the community, Jacksprat! This is an interesting question because it depends on what you will be using MODx for and what your immediate needs are.
There’s no reason why you couldn’t learn on both - if you need to roll out sites to production sooner rather than later than I would recommend focusing on 0.9.6 in the short term, at least until Revolution has reached RC status. The knowledge you learn wouldn’t be wasted because it’s definitely not the intention of the team to just drop 0.9.6 once Revolution, but rather development of the 0.9.6 branch will continue for a while yet (security patches/bug fixes/minor feature additions etc.) - and so much of that knowledge would be transferable to Revolution.
In that respect, there’s no reason why you couldn’t learn how 0.9.6 works (e.g. snippets/modules/chunks/plugins) and then transition over to Revolution to see how those same elements are applied in the new core and start learning the additional features that will be part of Revolution.
But, like I say, depends on your needs. If you don’t need to urgently roll a site out then get stuck into Revolution and help us with finding bugs and testing - that would definitely help get Revolution closer to release status
MODX Staff