Some decent routes. There are some good routes skirting the Clwyd river if you want flat headding out towards St Asaph and also some hilly aspects going towards Abergele, and more over to Rhudlan. Stick to some of the smaller roads and you won't get much traffic.
I used to come out of Preststyn along the Dyserth path, into Dyserth then out the back towards Tremerchion, then loop back via back of St Asaph and down to Towyn then back through Rhyl along the coastal path. Don't use the main road between Rhudlan and Abergele as its fast, busy and narrow. I tend to loop out by the hospital/St Asaph. Some decent cycle lanes between Dyserth and Rhudlan, again main road busy but the shared path is decent enough.