If I currently get TV via the antenna on the roof of my house who do I select as my provider for my Apple TV

You don't need a provider in that sense as such (except in the case where an app is tied to the content of a cable service - I don't know whether the ATV has such). You just connect the ATV to your internet connection via your wifi network or a direct ethernet connection to your router, and you will then be able to access the iTunes video library, some other streaming services (depending on your country - the BBC iPlayer in the UK for example) and, just recently, the Amazon Video library (both that and iTunes are pay per view, or Amazon has a subscription service, Prime, which give you free access to some of the video library plus free one-day delivery of purchases).

To elaborate, those apps require a cable provider in order to access content that is tied to a cable subscription. If you are only accessing OTA channels via antanna then you don’t have a provider and won’t be able to use those apps.