I'm not really sure which would be better between the 9550 and the 6200. The reason being that the 6200 in question has a 64bit memory interface which will cripple it's performance compared to a 128bit memory version. Also, I can't find any listed core or memory clocks on the xfx 6200 in question, so it's hard to guess how it will perform, although it has ddr2 memory, so I'd assume it has a higher memory clock than a card with regular ddr, but you never know...
The 6200 would have more advanced features, since it's newer, than the 9550, like shader model 3 support.