Cotton or Wool?

For such a long time I've wanted to make a Ripple afghan. For years though I've been more of a "finished object" knitter / crocheter instead of a "process" one. Meaning, that I was happier getting to that end result or product rather than just enjoying the process of making. A ripple afghan is seriously no project for a person that just wants to hurry up and get it done already. However, recently I've become much more of a process knitter. It's become a time for me to walk away from all the other stuff that I have going on and really meditate. And it is such a meditative thing to do. I don't really have to watch my hands anymore or count if I'm working on something simple. I can sit, knit and just "be" for awhile. My hands moving of their own accord, in such a repetitive relaxing way, it's so utterly soothing. So, I'm thinking now may be a good time to dust off my trusty hook and start a Ripple. My first hurdle though is trying to decide whether to use cotton or wool yarn. A quick Flickr search yielded some incredibly inspiring Ripples and the yarn was about evenly split between wool and cotton, so no help there. We are finally coming into the warmer months and the thought of a giant blanket on my lap made from wool makes me feel sweaty. On the other hand, the winters are so long and cold here, it would be very nice to have a wool blanket to cuddle under. So, I haven't begun and I'm already stuck. Dear friends, any suggestions? Which would you recommend?