AAA, and if you apply to unis that want a fourth AS just take an extra one in your final year. There's less pressure on you to get AAA in your A levels with those grades as you'd only need Bs/Cs in A2 (depending on how high/low the As were) so you can still finish with AAA and a decent AS level.
I took 4 AS levels but one was Critical Thinking (school made us) UCL said it didn't count so I took Psychology AS in my A2 year. My offer was AAA with a 'pass' in the AS level. As long as you take another AS before you start you're fine.