I have both the C110 and Carly, both work well enough if it's simply code reading/clearing you want but I've found the C110 to be pretty slow to use and often takes a while to move between screens and don't think it's capable of reading as many modules as Carly, but it is significantly cheaper!
The strong argument for Carly would be it's ease of use and ability to perform coding but at £100+ for the adaptor and app it is quite pricey, it is also a bit hit and miss on 'live data', this function doesn't work on my 3.0si N52 engine which is annoying as it's the main reason I bought the bloody thing!
The 'free trial' for Carly is useless, will only be usable if you buy the full version of the app... and even then there are 'add ons' at further cost. I've heard good things about the torque app mentioned by srhutch so that could be the way forward if you wanted to use your phone as a fault code reader