I've heard a few, not a fan of most of them. The original songs are already so perfect the way they are. Though I do really like Smooth McGroove's acapella covers.
I tend to ask that when I find anyone who likes Undertale as an ex of mine(who's still a pretty good friend) made a remix of Bone Trousle that I did some artwork for and it's always curious to see if they've heard of him. XD
I do have to agree though, I enjoy all the original pieces so very very much already. <3 They need no tampering.