What do you have by them? Personally I still think that their debut full length Mogwai Young Team is their best album but I have seriously never been let down by anything from them. Mr. Beast prob has my favorite Mogwai song "Glasgow Mega-Snake." That song is so fucking sick it's not even funny.
Their Government Commissions: BBC Sessions 1996–2003 is a live album that you really can't do without if you are a fan of them. EP+6 has all the songs from the hard to get EP's and is really good.
they have moments that blow me away and alot of other times they kinda bore me but overall I think they're a quality band
my personal favourite album is Come On Die Young