The only thing that makes a month best or worst in Snowdonia is the weather, so from that point of view July and August would be the warmest and driest, but also of course the busiest. The coastal beaches are at their best at this time of year too, with destinations like the pretty Porthmadog and its unique Brynkir Tower offering comfortable boutique accommodation. Try also going more out of season, as May to early October are all magical times to visit. Dedicated walkers make the most of the national park all year round. The magical village of Portmeirion is perhaps the ultimate North Wales coastal place to stay.