Funny how similar these two are. I felt that Splice was just a cheap knock-off version of The Fly whereas Species was a cheap knock-off version of Alien (possibly with a dash of Basic Instinct thrown in). I suppose Splice had a bit more substance to it (or at least tried to, despite irritating characters and that god-awful slasher ending) whereas Species was always going to be a guilty pleasure at best. Splice wins.