Not fished Llangennith yet but i would imagine peeler crab would be good for the bass and lug/rag for flatties.
As for which part of the beach i'd say you'd be better off walking up the beach towards worms head, mainly to get away from the surfers.
Nightime is probably the best from what i've read here, at least the surfers have gone.
When u going mate I might go sunday the best baits are lug maddies razorfish and crab hope this helps park in the caravan park and walk through the sand dunes and pick a spot if your going sunday give me a pm and if I can help I will
I fished there Tuesday and caught a few nice flounder, I read up the best place to fish it was by the stream that runs out 3/4 to the right of the beach and use worm baits and razor and crab. Hope this helps mate
if you aint fished it before park at hill end caravan park (easy access to beach,for bass fish night tide to high with lug razor baits,dont bother with crab unless you fish either island on the rough.my favourite wat to fish genith is when the g greys arrive late june onwards but September being best with maddies rod in hand no stand.