Gosh - I haven't done the French side so cannot do a direct comparison. I've done the English side several times. It would be helpful though to know their planned course from La Coruna - ie are they staying coastal and hugging the French coast or will they go straight across to Falmouth? The latter is further but has the benefit of being further from the hard stuff if the wind
pipes up and is probably actually quicker.
Both sides have their dangers and their opportunities, what with races and headlands and rocks and so on. I would expect any professional crew to be able to deal with it but it is complex, so check they have the right tidal tables and so on, and know how to use them. Both sides have some serious tidal races which must be managed both to pass them at the right time and possibly at the right distance (especially Portland
Bill) - and if they get it wrong either coast will offer a lot of current
Both sides also have lots of harbours and places to hide in bad weather
so easy stopping if needed.
There is very little to choose between the two sides in terms of weather
- after all once you're off Start Point, France
is never more than 70 miles away and any decent size Atlantic depression will cover both sides. I guess you might be marginally more to windward on the english side in a south westerly, but there's only a little in it.
To be honest, if they're a crew with any experience, I'd ask them which coast they know best and expect them to use that one - if they coast hop at all rather than sail right up the middle! And if they do the latter make sure you have a good radar
reflector, and preferably radar
on board. Whichever route
they should have good access to weather forecasts, through (at the minimum) navtex and vhf