Boqueria or Casa Mono?
What is the better tapas bar for a date during the week?
I've only been to Boqueria once, and Casa Mono many times, and I think the food is much better at Casa Mono. Though - the mushroom croquetas at Boqueria were fabulous. Can't speak to the date part, but Casa Mono is crowded and, I imagine, noisy. (I've only been for lunch.)
Boqueria has more traditional food, more romantic atmosphere (by just a tad), and is much easier to get into. Casa Mono has better food and a more ambitious menu. But it's much more cramped, noisy, smelly (due to open kitchen and layout).
I think Boqueria is probably better for the scene and atmosphere. Casa Mono is probably a better location for after. Food at both are great but probably like the food at Tia Pol or Txkito better. Probably in for a wait at Tia Pol Boqueria and Casa Mono but you should be able to get a table pretty quickly at Txkito.
Casa mono has much better food, with portions that are larger than tapas (called Racions), and they take reservations. Boqueria does not take reservations. Both can get jam packed, but I agree that Boqueria edges casa mono in ambiance.