I don't really like it either. I had a very large and ferocious gruff black dog named
Garth when I was small, so it always sounds kind of onomatopoetic to me, like the bark of a very gruff but loud dog. Apart from that, the G sound silly and the Gar sounds gaping and primitive, and the
Garth without anything after it sounds abrupt and makes me giggle. But my reasons for not liking it are purely phonetic. It's a good practical name.