Some of it comes down to the layout of your home and most suitable pipe route.
There are also two types of booster pump. The most common has twin impellors. One for hot and one for cold. the advantage here is that it gives a balanced hot & cold supply that is largely unaffected by water use elsewhere in the home. As well as pumping the hot water they also need to be connected to a stored cold water supply.
The other type just pumps the hot water and uses the cold mains supply directly. These can be prone to temperature and pressure fluctuation, although a good quality thermostatic mixer can keep the temperature stable.
A remote pump usually involves more plumbing as pipes have to be routed to the pump and then from the pump to the shower. Having said that the pipes are usually out of sight inside an airing cupboard and are easily accessible.
Some remote pumps can supply two showers.
Pumps can be noisy. If you have an early riser in the family, then where the pump is located may dictate that someone else has disturbed sleep when it operates.
Remote pumps can be easily changed in the event of a failure. Those mounted over the bath may be more difficult and require redecoration and / or repairs to the tiling if they need to be changed. Particularly if the pipes are buried in the wall and need to be relocated.
Then there is the aesthetics. A remote pump may be coupled to a stylish mixer and shower head in the bathroom (or even an existing one). Over bath booster pumps are a different matter.
If you are going to DIY, wiring an over bath booster will requires notification to your local council building control, and payment of their hefty fee. You don’t need this if the pump and any wiring is kept outside of the bathroom.
Finally cost, an over bath booster pump will probably cost less.
