The development progress has slowed significantly because the company previously behind armory stopped working on it.
I disagree.
Armory was stagnant for well over a year under ATI. Yet, as soon as they folded and goatpig created his branch, there has been a surge of steady progress and the technological gap which once existed between Armory and other Bitcoin development is almost closed. I would go so far as to say that Armory is working better than ever.
If goatpig would just remove the horrible auto-bitcoind code (which was a mistake to begin with), a large portion of user issues would vanish.
I do not recommend that you use Windows. Armory works better in a Linux environment like Ubuntu.
I disagree again. While I haven't noticed any significant differences with Armory itself, the only operating system which ever gave me issues with Bitcoin Core was Ubuntu. Windows, however, has never given me any issues what-so-ever with Bitcoin Core or Armory.