In my opinion, 刮 could be more widely used than 剃. 剃 means that you need a tool (specifically a shaver or a razor) to trim something. For example, 剃头(have one's head shaved); 剃胡子（to shave one's beard off） When we talk to 刮, it could also be used in the last situation, like 刮头, 刮胡子. However when it comes to an action that has nothing to do with the shaver or the razor, as 刮掉门上的油漆(scrape paint from a door), here 刮 couldn't be replaced by 剃. Hope this could help you ^^

刮 means to shave like there's no tomorrow with this "leave no one alive" attitude, the blade touches the skin during the whole hair-cut, while you hear screaming sound of enjoyment in the background. 剃 on the other hand means to trim, although it still can mean the same thing as 刮, but it is much less sever. if i say to my local barber that I want to 刮头, he will take out that big ax and start to peel off my skin without asking any questions. BUT if i said to him i want to 剃头, then he will ask me, how short? Hope you get it, :-)

一般人们说“剃头”、“刮胡子”，也有人说“剃胡子”，但这时他的胡子可能已经留了很长了。很少有人说“刮头”，除非你本来是光头，头发稍长出来一点，现在想把头再刮成光的，这时可以说“刮头”。所以你应该能感觉到，说刮的时候一般毛发非常短，而且刮完的结果是光的；说剃的时候一般毛发比较长，而且剃完后不一定是光的。 另外，“刮”的意思比“剃”要多，比如“把墙上的脏东西刮掉”，这时“刮”相当于scrub, “剃”是没有这个意思的。