I've only used CaptureOne express 6 being given free with Digital Camera this month, you can also find the free code on the internet, posted by someone from DC. I'm not too impressed. On pictures that don't need much it's ok, and the quality of the processed image somehow feels smoother and finer but there doesn't seem to be much flexibility. I tried some very dark images that ACR rescued quite comfortably and I couldn't get any where near with C1. I found the interface uncomfortable and had to open the image in PS to really see what I'd got. It also kept crashing.
This might all just be me of course. I've used ACR for so long now that it feels very straightforward to me. I'd try using the free version of Cone6 or you can download a 2 month free trial of 7 Pro which is probably a better idea. It's very expensive compared to the alternatives but it might work for you. I wouldn't buy it just on recommendation.