Funny you should mention it. I just got back from a lovely day's flying over all Wales, and felt like telling someone about it. I think I've flown practically every route there is from one end of the country to another, so...
The route down the coast is beautiful, and it's really easy to find your way. Keep a look out for the TV mast just south of Caernarfon, and the danger area by West Wales (which is no longer military Aberporth, so it's cheap to land there.
). You'll probably want to refuel at Carnarfon, nice airfield, food, museum, beach, and very easy to find. Down south you have a choice - West Wales, Haverfordwest, Pembrey, Swansea. I found out today that West Wales is very friendly but doesn't do food, and that Swansea is closed on Tuesdays and Wednesdays.
Pembrey can be awkward, as it's right in the middle of a danger area, but I was there once years ago, and it's a nice place. In fact, I'd recommend any of those. BTW, you may lose London Information when out near Strumble Head (lovely views!) so don't think you've had radio failure.
The other route you mention is fine too, but I think it'll be quite a bit longer, depending where in South Wales you want to go. Refuel at Caernarfon, as it's a long way from there to Welshpool. Liverpool are good for FIS when along the North coast. The only other airfield is Hawarden - £15 landing fee and no food.
Welshpool and Shobdon are both nice, though both a little hard to find - both have one shortish runway and sorrounded by hills. And mildly challenging to land if you're not used to shortish runways surrounded by hills!
There are other routes which don't involve tackling Snowdonia, which is no big deal on a sunny day with high cloud and no wind, but otherwise can be quite challenging. You can fly down the coast to Aberystwyth, then follow a convenient railway line to Welshpool. That's the route we took out to the coast today, since the weather wasn't quite as good as expected early on. Lovely scenery, following the valleys, and nothing much over 2000 ft. On a nice day, look out for other traffic flying that route though; it's popular with Welshpool based pilots. There are other routes across mid-Wales too, and you can navigate by railway lines and wind farms, which is quite easy. And although you could do with a 3000 ft cloudbase, none of it is as high as Snowdonia.
Today we left Sleap, heading for West Wales. As soon as we got to the hills there was low cloud and haze, so we dropped in to Welshpool. By an hour later the weather wa better, though still hazy, so we followed the railway line to Aberyswyth, then the coast to West Wales (ex-Aberporth). We phoned Swansea, who said they were closed. it was getting a bit late by then, so we flew round the coast...down to Strumble Head, St Davids, Milford haven...then up to Carmarthen. We then followed the railway line to Builth Wells, then a short bit of real navigation over some rther bumpy hills to Shobdon for a very late lunch. We then followed another railway line to Shrewsbury, the due North back to Sleap. I mentioned to my co-pilot that railway lines weren't really there for passengers; their primary purpose was to make nav easy for two pilots out on the first long flight of the year, who didn't really want to have to do any work.
It was lovely, a fantastic day's flying. Enjoy it when you go.
Right, that's about all I can think of. Now, tell me about flying to the Isle of Man, which is something I've been meaning to do for years.