Hi - I would take lit if I were you. Unless you find Lang particularly interesting, Lit is much more respected by universities. Lit is 1) in my opinion, more interesting 2) Most of the universities you will be aiming for with those levels require you to have taken lit, whereas lit and lang combined may not count. Have a look at the uni websites, but I would take lit.
That being said, if language is your thing and you find it really really interesting, go for it. But if you're considering an English degree and you particularly want to take lang, I would take it as well as lit separately (as in 2 a levels) - because Lit alone is the essential one (+ it is also useful for history/law degree etc.)