I went with a standard PS4 over the Pro as I found it better value especially with the bundles that were around at the time.
As for the old ones being obsolete, both MS and Sony have done clauses for development on the system so the games can be enhanced for the higher models but must run properly for the originals.
The newer ones are for those that seek an upgrade and will offer a better framerate and/or more detail. Online however everything will be set at the same framerate so no advantage will be achieved there.
So if having the top-end isn't important to you and you don't mind the odd game at a lower framerate then go standard.
How important the benefits are are ultimately up to you.