Which one is better?

Solution
That's not really a suitable upgrade, you wouldn't gain much performance, especially as you'd be downgrading VRAM.

A GTX 750 TI or maybe a GTX 750 SC would be a good upgrade for about $130 to 150. I wouldn't go any lower than that or it wouldn't even be worthwhile.

An R9 270 for $180 or a GTX 660 for $180 would be a very good upgrade, but substantially more than you planned to spend. A few of each class of card get as low as $170 on some sites.

Edit: Found a 2GB GTX 660 for $160 as a limited offer.
http://www.ncixus.com/products/?usaffiliateid=1000031504&sku=94940&vpn=GV-N660WF2-2GD%20REV2&manufacture=Gigabyte&promoid=1078

Also found a 2GB R7 265 for $150, which isn't quite as strong as a 660 but pretty close and still...
That's not really a suitable upgrade, you wouldn't gain much performance, especially as you'd be downgrading VRAM.

A GTX 750 TI or maybe a GTX 750 SC would be a good upgrade for about $130 to 150. I wouldn't go any lower than that or it wouldn't even be worthwhile.

An R9 270 for $180 or a GTX 660 for $180 would be a very good upgrade, but substantially more than you planned to spend. A few of each class of card get as low as $170 on some sites.

Edit: Found a 2GB GTX 660 for $160 as a limited offer.
http://www.ncixus.com/products/?usaffiliateid=1000031504&sku=94940&vpn=GV-N660WF2-2GD%20REV2&manufacture=Gigabyte&promoid=1078

Also found a 2GB R7 265 for $150, which isn't quite as strong as a 660 but pretty close and still significantly stronger than a 7750 or 7770.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814127790&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=3938566&SID=
 
Solution