Edinburgh's certainly worth a visit - the castle's well worth a look, there's good night life and plenty of shopping opportunities. Eilean Donan castle, near Kyle of Lochalsh, is probably the most picturesque in Scotland (see http://www.eileandonancastle.com/) and is about 2 hours drive from Aviemore. Kyle is also at the Skye bridge so I suppose you could take a trip over to the Talisker distillery. Aviemore's not too far from the Dalwhinnie distillery either but it's more of a ski resort than anything (if there's any snow) and I suspect Dunkeld might be a better base for distillery visits.

Glasgow's very lively with good museums and architecture and isn't quite as touristy as Edinburgh - I would probably go for the Grosvenor hotel as it's right in the West End and where I tend to gravitate to when visiting. I wouldn't voluntarily go to Bellshill for a holiday, or Dundee for that matter, although I'm sure I've offended somebody with that.

As for season, I prefer Spring or Autumn as they're a bit less busy although they could be a bit cold and wet for some folk. They also have the advantage of fewer midgies which can be an issue in the West Highlands particularly.

If you're not absolutely set on Hiltons, then Orkney's a great place with plenty of historical stuff to see, 2 distilleries and a good atmosphere.

You might want to have a look here to get a good idea of distillery distribution - http://www.whisky-distilleries.info/...eMaxi_EN.shtml in case there were any whiskies you were particularly interested in (NB, don't call it Scotch when in Scotland - you'll put people's teeth on edge).

If there's anything else you wanted to ask about, let me know!