My a-levels were six years ago, but ok. Hardest to easiest;
Psychology - loads of cases and random info to remember, and I didn't find it that interesting so I struggled to force myself to memorise it. Chemistry - Big jump from GCSE, from what I remember. Not too difficult, though, really, just slightly harder than bio/maths. Biology - Not really difficult either. Maths - Easiest by far, because I found it the most enjoyable.
You put psychology above maths/chemistry/biology? wow that is so weird.
Media Studies, Critical Thinking, General Studies, Photography....... LOL JK In all seriousness: Chemistry Biology English Literature, only did till AS though Maths History Computing (Just huge work load)
1) English Literature - I don't know, I just find it difficult 2) Politics - It's in the middle. Not so hard as English but easier than Media and Politics 3) Media - In reality it's par with Economics. It's quite easy 4) Economics - I find it the easiest by far, there's much less to learn compared to other subjects