You pretty much have a choice between:
Android
Windows
Blackberry
Apple.
If you write off Apple and are having problems with Android, there's really only Windows and Blackberry left. Personally, I liked the Blackberry tablet I used briefly in 2012, but I've no idea about their new OS or what their future is likely to hold. I've never used a Windows tablet.
Both of those are likely to suffer from a lack of interesting apps, but I believe Blackberry now let you install Android apps too. There seem to be plenty of Windows tablets like the ASUS Transformer, but I don't know about Blackberry.