Trying, and failing, to be remotely objective - there is only one answer here. Conwy is very good but RSD (of which - full disclosure - I was President until about a month ago) is a class above. It's also currently in fab condition, not least (which you might want to be aware of) as the Welsh Championships (male and female) are being played at Harlech at the end of this month. Do have a look at Ran's RSD profile on this site.