Lucky to live 7 miles From Llangollen so I am biased to NWales
Lovely roads and scenery, can be much like Scotland only on a smaller scale
Less midges
I know where the tea stops are
If you pick the right routes, on the right day, they are glorious otherwise you will hone your overtaking and filtering skills on the main A road against holiday / sunny day traffic and a flock of twats on sportsbikes....seems to attract the knobs
Lots of very good cut through roads and many single track ones
The link Wapping kindly provided shows a map covering a lot of North Wales routes. If you can that into a map program and take a look on G Earth to see what they are like. You can mix and match a lot of them
Few Police around. I know everyone thinks N Wales is swarming but it it ain't, same with the camera vans. But some of the camera operators now have a plain estate car and do hand held checks in villages, very hard to spot sometimes
Obviously Bank Holidays, very good weather there may be few extra ones out on overtime to do the bike operation whatever they call it this year, but if you pick your roads it should be fine.
I'm lucky, I can go out midweek, tend to avoid weekends. Somedays the only Police you will see all day are in the towns
If you factor in Mid Wales as well then you will never run out of excellent routes
One of my favourites is the B4374 from Aberystwyth to Rhayader which becomes National cycle route 81 You can turn off this 3/4 way along towards from Aber and follow the reservoirs to the Elan Valley dam - Not only sheep to contend with but lycra clad hoons
So many choices
My knowledge of S Wales is limited main roads to Cardiff / Swansea etc, which are nice in a car