Bordeaux is primarily about place, secondarily about time. Other considerations, such as grape variety or winemaker, are deemed trivialities and demoted to the back label; you buy a Pauillac 2015 or a Saint-Émilion 2010.
Here, the grape is merely an expression of the soil and ripening conditions of the year, the winemaker's role more technical director than visionary.
They say in a good year you buy the second wine and in a bad year the first wine; that is exactly what we have here - in a sense; a lesser appellation from a better year vs a better appellation from a weaker vintage.
As to which is better, the market and / or accolades can often tell you what you need to know; the Medoc is a Cru Bourgeois priced at almost double that of the Blaye.
If, like Richard Bampfield MW, you drink pretty much exclusively reds, the juicy, Merlot-dominated Blaye could be your aperitif / starter wine, with the textured, Cab-dominated Medoc accompanying main and cheese.
Château Les Martins 2014, Côtes de Bordeaux, Blaye (£9.49, Waitrose) fresh with bramble and cherry fruit, liquorice, spice, pencil shavings and fine, gentle tannins.
Adept and will age further.
We matched this with toasted ciabatta, rubbed with garlic and tomato topped with basil, tomatoes and olive oil.
Château Poitevin 2012, Médoc Cru Bourgeois (£17.95, Lea and Sandeman) minty-herbaceous with dark bramble fruit, leather and complex oaky spice; fresh and inky with a dense muscular core. Supple with firm, fine tannins.
Still very youthful and primary; will repay cellaring.
We matched this with aged, Aberdeen Angus rib steak (rare, of course).