USB2.0/3.0 vs nas

Hello..

Need tips for my storage problem.

I dont have anything atm, so cant abuse any old stuff..
Primary htpc is gonna be(getting it this week) Shuttle XS35GT-V3 (up 24/7)
Secondary htpc will also be XS35GT-V3.
I also need to buy someking of wlan router no matterwhat.
I only need like 2-3TB shared storage and i will stream 1080p content from that this one.

So the question is:
Is router with usb port+external usbdrive enought for this or should i go for somekind of nas?
Also would like tips for good router.

-Samo