Cologne is a huge interest for me and I do what I can to expand my horizons (because it competes with the head-fi budget!). The one big catch here is that, just like with headphones, my senses are probably only very sharp and perceptive in certain parts and totally dumbed down in others. I think I do have the nose/ear that allows me to be particular when it comes to these things, but I can't really, for the life of me, single out the individual notes/frequencies, in spite of having had aromatherapy as my training wheels for over 5 years. So the learning continues...
I guess my criteria over the last 6-8 years has been to avoid a certain cologne archetype. I get the feeling that I don't want a "proper" or "traditional" masculine cologne. I'm not sure where that impression came from, could be my dad going through three bottles of Egoiste, could be the Brut or Blue Stratos I've always seen around the house as a kid... but this is how I ended up wearing Narciso Rodriguez For Him this past year,and Paco Rabanne's BlackXS before that. And I'm sure that's why I couldn't commit to Terre d'Hermes in spite of how good it really is.
Having done that I guess I'm looking for more visceral/blatantly sexual scents going forward, just to further my idiosyncracy
I almost bought YSL Kouros last month, if you know what I mean...Asian, pale, geeky, meek, to spray Kouros all over that... LOL. I guess I'm also avoiding the one bottle I've always admired: nevermind my idiosyncracy, I absolutely loved John Varvatos when I sampled it at a Sephora, but that was five years ago, and I haven't had the budget to spend $100 based on a partial impression that's no doubt eroded over time :P
I don't think I can name an all-time favorite yet, I seem to like everything... everything that's not by Issey Miyake at least.