Is Ubuntu easier to use than Fedora? Is the support community better? Would MythTV, NDISwrapper, and VLC work better with Ubuntu?
That depends on your perspective. Ubuntu and Fedora both have fairly large, newbie-friendly communities. As to which is easier, it really depends partly on which one you are familiar with. I tend to prefer Ubuntu because I'm a Debian bigot and like to dump on Fedora and Red Hat when I get the chance.
But, in general, I'd say they're pretty close. Ubuntu has the slight advantage in having significantly more packages in their official repositories (the only external repo you'll likely need in Ubuntu is Medibuntu). Also, yum is not as good as apt yet. Don't get me wrong, yum is a huge improvement over just using rpm, but yum is slow (and it has little to do with it being written in Python). Fedora has a fast release cycle, and tends to run bleeding edge stuff. It is convenient if you tend to use RHEL systems too, because the layout and tools are the same.
The hard part of MythTV is generally setting it up, independent of distro. ndiswrapper would probably be easier in Ubuntu since it is included directly in the default kernel packages, and VLC would probably be a wash (you'd need an external Ubuntu repo to get libdvdcss).
If you do need NDISWrapper then just Google for "ubuntu ndiswrapper".
Ubuntu actually bundles ndiswrapper directly in the stock kernel packages, so all you need to do is install "ndiswrapper-utils-1.9" tools package.