They’re not exclusive and a good network will likely have both (and more), at least in a somewhat large city: trams are much slower and compete with others for above-ground space. Their frequency is also limited by the need for other users of the above ground to use the share space.
Trams are also not able to deal with high gradients, unless they’re hybrid rack rail, or they’re trolleys rather than trams.
Finally, metros commonly have above ground sections or lines (which is why that’s a better name for urban rapid transit in general).
The advantage of trams for cities is that they impede cars on the narrower smaller streets, which helps to enforce speed limits and flow. On the wider streets trams will have dedicated lanes wherein they can just pass the vehicles stuck in traffic.
Trams are also not able to deal with high gradients, unless they’re hybrid rack rail, or they’re trolleys rather than trams.
Finally, metros commonly have above ground sections or lines (which is why that’s a better name for urban rapid transit in general).