House vs Flat? How did you decide?

The UK has a massive crush on living in a house even if this often comes with higher operating costs, more hassle, higher price/sqm and longer commute times. However, 46% of the EU population lives in flats and in nations such as Spain, Germany and Italy living in flats is the norm. I personally find London quite strange for how low it's density is compared to cities such as Paris (metro area), Munich or Madrid.

How did you decide between the two options?