Best recommendation for a Carneddau traverse, is to park in Gerlan, just above Bethesda.
An approach to the main Central ridge, taking in the summits of Yr Aryg and Bera Mawr, is the stuff of dreams in fine clear weather.
From Yr Aryg, you can quickly gain the main ridge itself, and the route towards Foel Grach and Carnedd Lewellyn is very straight forward.
Distances are quite deceiving, as reaching Foel Grach from Gerlan is quite an undertaking, but the rewards are immense.
April is a nice time of the year to venture into the Carneddau, but avoid parking in Aber, as gaining the main ridge is far more rugged, and does not offer the same enjoyment as an approach from Gerlan.
Which ever route you take, its a majestic walk, possibly in the top five best walks in Snowdonia.