Sounds like a fine idea Ms V.
I reckon it's got to be twixt Castlerigg and Long Meg. Really, for folks making the journey from afar, who've never seen either, they'd have to see both. Though I'd reckon Long Meg would be better to spend a couple of hours at for a collective blether, (less busy, bigger and there's Little Meg too) then nip down to Castlerigg for a quicker look-see, possibly stopping off at Mayburgh.

Then if folk were up for spending the night in Cumbria, a visit to Langdale, offering the opportunity for Copt Howe and a glimpse at the Pike O Stickle, as it would give an excuse to stay at the ODG (or adjacent campsite).