Converting 720x480 to 640x480 square pixel ...?

I've got an NTSC video, 720x480 29.97 that I want to convert to 640x480 square pixel.

I used Compressor with two settings, with resize and retiming Better and Best.

Both Compressor settings give me a decent output but throughout the video there are "blips" (certain parts of the picture bulge a little for a frame) in certain scenes. You would expect theses scenes to be heavy motion but some are not where the camera isnt moving.

Whats the best settings for converting down to 640x480?

(ps: I keep the same frame rate, 29.97)