Clockwise = Steep as hell 30+ minute carry up Y Das, 5km easy descent down the other side.
Anti Clockwise = easy 5km climb up to Y das followed by a mental steep & rocky descent that you'll either ride down, fall down or walk.
Depends how you like your ups 'n' downs really. Last time I was there we skipped Y Das as it also had some sheet ice thrown in and was a ticket straight to casualty!
Whichever direction you decide on, at some point you'll wish you did it the other direction, so best plan a return trip now to do it the other way 😉
Other rides? get the map out, it's actually quite difficult to pick a bad route over there.
Check here for ideas http://www.mtbbreconbeacons.co.uk/