In reply to Felix Ottey:
I would do the classic routes, but stay away from St. Govans if you can. The HVSs there are really steep, really polished and feel hard for the grade - and they're just crap compared to routes on the more adventurous crags. I thought
Riders on the Storm (HVS 5a) was a fantastic HVS,
Bludgeon (HVS 5a) is good - both have fun scramble approaches. As offwidth says, if you want to climb slabs (or specifically steep slabby walls) you won't find much in the South, you need to head to St. Davids and explore the sandstone (which is like climbing slate but with friction).
Carreg-y-Barcud Area is the biggest crag of the area and has fantastic routes in this style,
e.g.
Ethos (HVS 5a). If you fancy pushing your grade,
Sinecure (E1 5b) is a really beautiful route and I think very soft for the grade - an all time favourite route of mine.