We use the wine that we’ve chosen to complement the meal and chilled or opened to breathe. Unless our guests ask us to open their gift because it’s special or they want to try it, fine, we’re not precious about it.
I think I would regard what my friends brought as a present and give them the wine I had already provided at the meal. We have relations who are likely to come for a stay bringing a bottle of champagne, in which case we do somehow manage to have that with them!
Well perhaps I should ask 'whose' bottle do I open. If I invite friends around for a meal, just a meal rather than a formal ' dinner' and my friends bring a bottle ..... do I open their wine or my own? (I'm sure this has been mentioned before but I've had a quick look around and can't see a post).