By games availability PS2 is best, the fat version is more flexible and lots of hacks for it, while the slim version has a much better lens / laser. LAN port is also built-in for the slim one, although you need some hacks or only original games would connect on Sony's servers.
For the fat one you will need to find a separate LAN adapter which lets you connect an IDE HDD internally as well for storing games / installing Linux to use the console as a PC although on the slim one you can use a USB HDD to store and play games only.
Wireless controllers are two piece devices, the antena connects to the PS2 port like an ordinary connector while the controller takes batteries and works wirelessly, you can find them for around Rs. 1000/- onwards. On the other hand PS3 has bluetooth controllers which do not require antennas to be pluged in to the console.
In Karachi I think check Abdullah Haroon Rd. and Khadda Market. A lot of people are selling second hand consoles and accesories at Pakwheels and OLX too.