The old page made sweeping claims about weather, value and crowds. Those vary too much by date and booking to be dependable. This rebuilt comparison focuses instead on durable differences a UK traveller can actually use.
THE JOURNEY
Road trip versus ferry trip
For Cornwall, the journey is predominantly a UK drive. Brittany introduces a ferry crossing but can reduce the amount of French driving if you choose Saint-Malo or Roscoff around the part of Brittany you want to visit.
THE COAST
Brittany gives you several different beach holidays
Northern Brittany, Finistère and the south coast feel markedly different. That makes Brittany particularly useful if the beach is only part of the holiday and you also want walled towns, markets, islands or a road trip.
COST
Compare your actual dates
Avoid assuming either destination is always cheaper. Ferry fares, fuel and accommodation vary by date and demand. Compare the complete trip for your dates rather than relying on a generic percentage saving.