Re: A'bunadh or Balvenie 12?
Of the two, definitely the A'bunadh; even though I find Batch 18 to be a little too winey, it's the sheer power and complexity that would make me choose it over the DW any day (although, of course, the DW is a great dram too...). As for adding water... part of the fun is finding out yourself! I tend not to add any, though a drop or two does round the rough edges if you need them rounding.
And as for other sherried malts, I'll recommend Glenlivet 18. I wasn't a huge fan of Glenlivet from the expressions I'd tried before that (12, 15 French Oak and a 15 G&M bottling), but the 18 blew me away for its depth and balance, and is one of my all-time favourite whiskies.