your opinion? Sonus faber Serafino Tradition vs the Focal Sopra 3

Focal will most certainly be more detailed. Some hear may hear excessive brightness. System/room dependent. YMMV

SF will have a subjective "warm/romantic" personality compared. Have not heard Serafino  but MANY others, assuming it follows the SF "sound."

I like both presentations. Prefer SF aesthetic.

The Italians taught the French how to cook. They have an aesthetic sense that is hard to overcome. Sonus Faber all the way! Compare a Ferrari to a Citroen.   

+1 tablejockey on the house sounds (like him I don't know the specific models).

Critics may accuse Focal of boom-tizz, and accuse SF of being insufficiently resolved or even unexciting.

My taste runs to the musicality-warmth camp, not the detail-resolution camp, so I've enjoyed the SF I've heard (I came close to buying), and found Focal a little fatiguing.

If your tastes are clearly in one camp or the other, that might well predict a preference.

As per @tablejockey ‘s post 

You didn’t state your musical tastes. I think that will play a big part in which ones you would prefer.