In reply to Gordon Stainforth:
I have Sierra running on both the iMacs we use daily and haven't found any problems that could be pinned down to Sierra.
I have had the search function in Mail fail a couple of times - but it did that on Yosemite as well. The solution is to get Spotlight to rebuild its indexes.
Similarly, Time Machine has a tendency to throw a wobbly if I make
any change at all to the Time Capsule configuration. It decides that it's never seem the time capsule disk before and initiates a length and unnecessary full backup. Again, it used to do this on previous versions of MacOS as well. I think there's a persistent problem either in Time Machine or Time Capsule. I suspect the latter, if for no other reason than that Apple are dropping
I obviously can't guarantee that some of the applications you use won't have problems with Sierra, for the simple reason that I don't know what you do use. None of the applications I use have had problems with Sierra, bar a few small utilities which I'd forgotten I even had until I spotted that they had the circle with the diagonal bar overlaid on their icons in the Applications folder.
In summary: I'm not aware of any issues with Sierra itself that would justify holding off upgrading to it now. But I would still make sure that I had an up-to-date Time Machine backup on hand before starting the process.