I am not super fussy about saddles and have happily ridden coast to coast on the saddles that came with a couple fairly low end bikes including one that a lot of folks bad mouthed quite a bit. That said , when I needed to replace a saddle a while back I bought a Prologo Kappa and was very happy with it. It was my favorite for a while.

I have a new favorite though... I loved the saddle that came with my REI Novarra Ponderosa 29er MTB, but the rails bent and eventually broke (riding a lot of bumpy singletrack). It was the lowest end of the WTB Volt line. So I replaced it with one from the same line only a little better model. I went with the WTB Volt Race 142 Saddle and if I were buying a new saddle for any of my bikes whether MTB, tour, or road I think I would go with another of these.