姑父 and 姑夫

I learned the word 姑父, meaning "uncle", on Chinesepod a long time ago. I've been trying to memorize this word, but haven't been able to. Just now I was thinking that the reason I'm having trouble is because the second character is 父 meaning "father", and 姑　is "aunt". 

I thought to myself, 姑夫　would make much more sense, and then I found out that 姑夫　has precisely the same meaning. 

My question is, is one of these two words used more than the other? Any other information about ?