Adding a netrowk card

I have a desktop PC and would like to add wifi. I know I can get a USB device, but an internal card would be more discreet. However, I'm not much of a techie so I don't know which socket type to get.

Here's a photo of the motherboard:

The PC has on-board graphics, and while I don't have any immediate plans to add a proper graphics card, I'd like to have the minimum fuss adding one later, if I do.

So which socket should I get a wifi card for? A quick look on websites seems to show they're cheaper for the bigger socket rather than the smaller ones, but I don't know if it matters which one I use.

And is it just a case of slotting the card into one of these sockets, installing the drivers and away I go?