In terms of size, feature, battery life and charge time arrow is a clear winner. In terms of sound you have more option adjust the sound with arrow so in that case it will win but if you leave it at default it is difficult to declare a winner. I would recommend C4 because it is is cheaper and sound the same and it will be a lot easier to obtained. Arrow sometimes require a month of waiting in order for you to get it.
I have been using my C4 ever since I have got it, due to the 2 Ohm output the lowest impedance recommend for this amp is 16 ohm however arrow is said to adjust its output impedance based on what is connected to it however I do not know how good of a job it does.