It is all subjective of course.
My preference has always been to play original material over covers. Don't mind doing the odd cover, but always think that there's more scrutiny on people playing covers, cue the "you played that bit wrong", "they didn't play it like that on the album", etc. comments (usually from the guitarist). But, I do like the challenge of coming up with a line that compliments the song, and adds something else to it as well.
I can see the gratification of playing covers, especially when gigging. Playing music that people know and will react to (whether you play it "correctly" or otherwise), is part of the reason why we do what we do.
Can't really say more than that.