-Modern Nvidia goes like this... G(lowend), GT(Low mid), GTS(high mid), GTX(high end).
-FX and Quadro are workstation cards and are not meant to game they are made for digital imaging and 3d rendering.
-Neither brand is really better but for every price range one may be the better deal.
In the sub $200 range I would get this for $195
or if that one was a little too close to budget this one for $155
Newegg.com - ZOTAC ZT-40404-10P SYNERGY GeForce GTX 460 (Fermi) 768MB 192-bit GDDR5 PCI Express 2.0 x16 HDCP Ready SLI Support Video Card
The 5770 is the better card straight out of the box but the GTS 450 can catch it with a good overclocking.
Refer to this thread for help and also google for benchmarks.
Graphics Performance List
EDIT: Found better card in budget.