It'll be the server that the system determines is best suited to route your request to the end point so quite likely one that's geographically close. Internet traffic might change it sometimes to a physically longer but less congested route. Basically whatever way gets you there the fastest.
If a site is not hosted on a single server but has mirrors across the globe it might also swap one for another sometimes, for example I'm connected to Stockholm this morning and first got served Youtube's Norway page but a couple minutes ago it changed to the Netherlands, and for all I now this afternoon it'll be France or the UK.