In reply to Cneifion Arête:
Of the grade 2's i've done in Wales, The Staircase and Byrant's Gully are both great routes but pretty high in the grade - especially when wet, which is most of the time.
East Ridge of Y Garn is a great route, and a good call. I climbed this for the first time in the summer by myself, with a loaded Bergen, in moderate wind. Provided it's dry and you've got a good head for heights (and the ridge isn't being whipped by a bad crosswind), i'd say this would be a good choice.
Bastow Buttress is another good call, despite it's grade 2+. IMO it warrants a straight grade 2. That said it is pretty steep and sustained though escape is never far.
I'd second the aforementioned Y Gully-Notched Arete combo. The Arete, in isolation, would be the ideal route as an intro to the grade. The trouble is getting to it. A grade 1+ approach is possible, though not at all obvious and probably best avoided until you've got some more route under your belt. That leaves V Buttress/ V Arete/ Y Gully as intros, the latter being the only one i've done. Y Gully was technically harder than the Arete, but still closer to grade 2 than 3 from what i recall. The two together make a great outing.
Milestone Gully would be a safe and easier option, though a bit on the short side.
The Braich Ty Du Face of Pen Y Ole Wen is, perhaps, worth a mention.
Cheers!