When I started knitting, I began with acrylic, because it was cheap and came in a load of fun colours. I was also drawn to fuzzy and eyelash yarns, which I'm really not a fan of anymore (I prefer something smooth that lets me see what I'm doing). Of course, while acrylic has its merits - in my experience it makes a fairly decent blanket - it's not the greatest, especially if you crave definition and want to do fun things like lace and intricate stitch patterns. It can't really be blocked, so if shape is an issue, it's not really the best choice.
I still like cotton, but I've realised that while it is good for some things, it's not for everything (again, see definition and shape issues; also, elasticity). I'm learning how to use it to the best of its ability (for e.g., I was thinking of using it to make a Caliometry, but when I realised that it would be floppy and not really hold shape, I gave up the idea. However, it worked for the Lana and Clark ascot, though probably not as well as it would have with the recommended fibre).
Which brings me to wool. I think I still have a holdover from my youth, where I think of wool as an itchy, annoying thing that overheats me and makes me feel yucky when I wear it. The more I work with it, though, the more I love it. It shows stitch definition, it's springy and elastic, it's lovely and warm, and it's just so very, very cosy! (Sometimes there's some residual itchiness but I'll imagine that it's more psychological at this point than actual.) Sure, I also love alpaca and other protein fibres, and I haven't really had the experience with plant fibres that I want to have, but for now I'm going to boldly go out on a limb and declare myself a wool woman. I reserve the right to change my opinion, but at least for today, I ♥ Wool!