Out of those the PS4 Slim.
The Pro doesn`t do anything the Slim doesn`t and costs more. I prefer PS games to Xbox (and Nintendo for that matter), so the S is out. And the Switch isn`t confirmed to have achievements yet so that`s out by default.
Have you really looked at the PS4pro' specs with regard to the PS4's (includes slim) specs?
Cost wise you are looking at a 500GB PS4slim being $300 USD compared to a 1TB PS4pro at $400 USD (original price of the launch PS4). While there is no 1TB PS4slim pricing for the US at the moment you could reasonably add $30 to $50 USD to the price.
You also have to consider that the PS4pro has a SATA3 bus (up to 600MB/sec) compared to the SATA 2 bus (up to 300MB/sec) of the PS4slim. In addition, it is over twice the graphic performance as well as 30% more in processing power and can display by smart upscaling and even native (depends on the game) 4K output.
Paying an extra $70 to $50 USD more is IMHO worth it and I am saying that as a PS4 owner.
The thing is no one is forcing you to purchase a PS4pro or PS4slim or any game machine for that matter the choice is totally up to you.