It depends on how far you want to ride?
I ride the elan valley a lot, but also ride around Llanwrtyd.
As mentioned above a bridleway on the map is no guarantee! I have found this out the hard way many a time!
One of my favourite rides in the area is riding from elan valley out to Claerwen dam and down to Strata Florida, then following the tywi track to the backside of the devils staircase, following the valley road to abergwesyn then using farm track bridleways into the forest at trallwm, over carnau back into elan. It’s a big ride at 60k ish and navigation is tough if not familiar with the area
I did a good ride a few weeks ago starting from irfon forest, took in the red, blue and black at coed trallwm and then back into irfon via Llanwrtyd for a 40k loop. A lot of climbing around 1500m so not to be underestimated!
Brechfa is worth a go also, especially if you link the gorlech and the raven together, only 38k but again some big climbs. I normally start with the red first and then pick the black up before the final red descent.