The floor and the orientation are two decisions that can never be changed later. Partition walls can be moved, the kitchen can be renovated, but an apartment with north-facing windows stays that way for as long as the building stands.
Orientation
South-facing rooms get light all day and are warmer in winter — and hotter in summer if there is no shade. East gives strong light in the morning and calms down in the afternoon, which many prefer for bedrooms. West gives strong afternoon sun, which in July means heat until late. North gives even but cool light and no direct sun.
In practice, the most comfortable apartments are those with dual orientation — windows on two sides. This allows cross-ventilation, which in summer is worth more than any air conditioner.
Lower floors
They are practical when you have small children or elderly parents, and they don't depend on the lift. On the other hand, they get less light, especially when the building opposite is tall, and they are more exposed to street noise.
Middle floors
Usually the best compromise: high enough for light and views, low enough to walk up when the lift is out of order. They also have the thermal advantage of being surrounded by other apartments above and below.
Top floor
It has the best light and view, and usually less street noise. But it is the floor that feels the outside temperature most, because it has the roof above it. Ask how the roof is insulated and whether there have been leaks — this is the most important question for the top floor.
The things people forget
Check where the parking space is and whether it belongs to the apartment or is shared. Check the position relative to neighbouring buildings — a new building opposite can take your light two years later. And visit the apartment at different times of day; what seems quiet in the morning can be completely different at six in the evening.