In reply to Cneifion Arête:
I've not done Idwal Buttress, but Y Garn East Ridge is a good bit easier than Byrant's Gully. They are both great routes. The gully is less exposed but much harder technically.
I climbed the gully solo in torrential rain, under these conditions it felt like a grade 3S. Despite or even because of these difficulties, the gully was an epically atmospheric expedition; a sustained and continuous line of weakness through Glyder Fawr's massive south face. Whilst the route offers continuous scrambling and some sharp obstacles, these two factors are rarely combined; the sharp obstacles aren't themselves that sustained.
In good, dry, conditions, the gully is - i imagine - still pretty tough. The latest Cicerone guide grades it a 2+ (the same as Bastow Buttress, Braich Ty Du Face, Ideal Staircase et. al.), which i'd agree with. There are various obstacles that are harder than you'd expect at grade 2.
The ridge is much simpler, even if the hardest route over the initial buttresses is taken. Most of the ridge is far more escapable, takes less drainage, dries quicker etc.
Greetz