Over the years we have always been a PlayStation family. (Had a PS1, PS2, then a PS3).
A couple of years ago someone passed on their old Xbox 360 to us. Agree that it's old now and an Xbox 1 would be better.
Last year dh got a decent bonus last November and we looked into buying the 4 boys a new console between them for Christmas. We took ages discussing the Xbox 1, PS4 and Nintendo Switch, weighing up the pros and cons. Asked in Game shop etc. for which one was best for different things etc. They said the main difference is the choice of games, Switch had more suitable ones for younger children, PS4 more geared towards older teens and adults.
It eventually came down to deciding between the PS4 and the Switch. As the boys ranged from age 7 - 16 we went with the Switch, just for the variety of games.
Even though we have always preferred the PlayStation consoles we have never regretted deserting them for the Switch. It is more portable and suitable for our now 8 yr old and 11 yr old.
One thing to take note of is the games. Have a look in game stores for the selection and see which ones are most suitable/relevant/desired by your ds. Some games are only available on PlayStation, some only available on Switch, some only available on Xbox. If your ds would like a certain game that is only available on one console you might want to take that into account. Our boys were interested in one game only available on PlayStation and one only available on Switch so we weighed up which one would be least disappointing to not receive in our decision.
Does your ds have a preference over which console?