Definitely the boost version. It is essentially a GTX 660 (non ti) with some shader cores disabled and will serve you better in the long run. I just upgraded from a GTX560ti to the GTX 660 and I am very happy with it. I wasn’t going to upgrade either but the low price of $169 USD was too tempting. It was essentially the same price as a GTX 650 ti Boost with all the shader cores so why not.
Windows8.1 Pro 64 bit, Antec EA650 Power Supply, ASRock Extreme 4 motherboard, I5 3570K processor, 8 gigs of Kingston HyperX 1600 DDR3 ram, Kingston HyperX 3K 240 gig SSD, Asus GTX660, Cooler Master Storm Scout case