A HD4550 is basically a HD4350 in drag. It is slightly more powerful but has worse build quality than the Nvidia card. Overall neither are that good for gaming. I do not expect you to stretch you budget, but a HD4650 or a GT220 will destroy the other two
If you are gaming even the HD4650 is a pretty poor choice. It will be acceptable at low resolutions but an HD4670 is considerably better and I would consider it the minimum if you are at all serious about gaming.