As mentioned before, try them if you can. I did and bought the C15. The reason I personally prefer the "C" models is that you can grip them higher up with your hand more in line with the axis you are drilling or driving on. This tends to give better control and a straighter approach but only IMHO. Someone who is a heavy user of an existing T model i.e. any other drill on the market, may not find this such a big deal but if you're a relative amateur, I do think the C is superior ergonomically.