HD6670 1GB GDDR5 > GT630 1GB GDDR5 > HD6670 2GB GDDR3
(you can forget about gddr3, regardless of extra 1gb memory it is a very slow card between those)
Well... 6670 ddr5 is the fastest of all. its not even open for debate.
here is a basic comparison between 6670 gddr5 vs gt630 gddr5http://gpuboss.com/gpus/Radeon-HD-6670-vs-GeForce-GT-630