In reply to duncan:
> (In reply to briantreanor)
>
> Grit is wildly over-rated. A visiting American writes:
>
> Suddenly it dawned on me that these boulders were the fabled gritstone. Dear Lord, I thought, the poor island and its inhabitants.
>
Grit is certainly peculiar, and I can't really imagine how it would seem to a visitor. If you live next to it and climb on it for years its easy to appreciate its magic. The gearless ankle-breaking micro-routes with a single friction move above a dreadful landing can, believe it or not, be amazing climbing experiences which live as long in the memory as as 10 picthes on an alpine face. But I think it takes a lot of getting into.
As such, maybe call in on the grit to see what it's like (and maybe prepare to do some bouldering) but personally I would advise against making it a big part of the trip.
By far my favourite climbing desitination in the UK is the NW Highlands of Scotland. Diabaig, Sheigra, Reiff, and Stac Pollaidh are the most beautiful crags I've ever climbed on. If you get the weather, the mountain crags offer a different degree of scale and adventure. The scenery is like nothing I've experienced anywhere in the world and the climbing is incredible and varied. The weather and midges are issues, but the coast (where many of the amazing crags lie) is often fine. I think it's really worth the journey. Better earlier in the summer.
As others say, North Wales offers a huge variety in a small area. Gogarth is a brilliant climbing destination, but it can be rather adventurous - and very rewarding. Often sunny when the mountains are wet. The slate occupies a similar appeal to grit: a unique, quirky, small-scale experience which some people love.
Pembroke is excellent - single pitch trad sea cliffs. Less adventurous than Gogarth, with more reliable rock, easier approaches and shorter routes, but the big pitches can still feel like a quite an adventure (especially if the tide's coming in at an alarming rate).
The furthest tip of Cornwall is fantastic. Sea cliffs on beautiful granite and some other interesting rock types offering single and multi-pitch climbing from the very scary and adventurous (e.g. in the Great Zawn at Bosigran) to much tamer accessible single-pitch stuff.
Sport climbing in the UK is not really as it is elsewhere. Plenty of very hard, very polished, very short routes, but there are no sport climbing destinations comparable to a trip over in Europe where you might expect to have 'fun' in a conventional way. Low-grade sport climbing in this country tends to be in unattractive locations and sometimes on appalling choss. Unless you want to try some hard, short, polished test-pieces I would say: avoid.
Hope that's helpful. Have a good browse through the photos on here for inspiration.