If both fit you well the decision comes down to what your plans are. I have the Tipperary and absolutely LOVE IT... as as schooling helmet. It's not quite as "space alien" looking as some of their past models, but still pretty modern looking and I don't show in mine. (I also show quite a bit, largely on the rated circuit) The ventilation is wonderful (better then any other helmets I've ridden in), it's very lightweight, but feels much more sturdy then any Troxel I've picked up. I love it. Again, for schooling. If your troxel is too shiny, you may not be happy with this one. -it's not shiny, but it's not a traditional helmet.
The CO IMO is more of a show helmet. They're classic, look wonderful, and very in style in the show ring right now. They're very comfortable (great padding) but there is no ventilation.
So the question is, would you rather have something that's got air flow and comfortable for schooling and just deal with it at shows? Or have a more professional looking helmet for the shows and just deal with the heat when you're schooling?