In reply to Sleepymouse:
It'd be better to walk via Daear Ddu if looking for a scramble, as others say, but even if you just parked near the Cyfyng Falls and walked directly up the main ridge North of the summit you'd still have a lovely walk with a slightly scrambly bit in places (entirely optional and avoidable). I'd say that's the dryer of the routes underfoot but it's Wales so I don't guarantee dryness anywhere
It'd be hard to make a wrong choice with Moel Siabod. Enjoy!
Post edited at 22:24