Windows is behind and not to take away anything from their efforts, I think it's going to be awhile before they achieve parity. My uninformed guess is about a year.
For many Gospel Library users, the key features are already in place--and for most others, I expect the remaining feature disparity issues to be gone within about 3 months--we're in the process of working on Notebooks features right now (which will most likely take Tags and Links along with it--and tabs will follow shortly after), which basically closes the gap for normal users.
Additionally, Windows already offers features that iOS and Android simply don't. Dedicated active pen support (for a more paper-scripture like experience when highlighting/underlining), support for users with dyslexia and visual impairments like Irlen Syndrome (OpenDyslexic and the sepia theme, respectively), inline notes, reference previews, a far easier to use Collections feature, the Inspirational Messages feature, and, of course, a dedicated
tablet UI, instead of a blown-up phone UI for a tablet.
I also have the Stream 7 and while it has it's nice points (like being able to run PC software), the on-screen keyboard sucks and it generally isn't as nice a user experience as the Nexus. But with Windows 10 coming out, this could change in a few months.
Not sure that'll really ever be the case. You definitely get what you pay for. $79 is peanuts in the tech world, and, though $79 gets you more than it used to, it's still not a great device. For those looking at getting a Windows device, I'd look at stuff like Asus Vivotab 8 ($180) at the low end, but recommend Microsoft's own Surface 3 ($499+) or Surface Pro 3 ($799+) at the mid- and high-end tiers, respectively.
I am looking to get a tablet and am wondering about the current state of the User experience on the two platforms. Personally I am not considering windows.
Personally, I'd like you to at least give Windows a shot, as there's some great stuff available with it, but I have quite a lot of experience with both iOS and Android. My two cents is this: go with iOS. Android is a mess, though it has made some baby steps in the right direction with its Material Design overhaul in Lollipop. Battery life is abysmal across the board, apps crash more often on Android, and are generally better designed on iOS. While iOS has fewer buttons, it makes better use of intuitive, easily-learned gestures, and is generally easier to use than Android. Yes, you can customize Android into oblivion, but unless you're a serial tweaker, you're probably better off just getting a better experience out of the box.