In terms of purchasing something to use with a sewing machine, stability is the #1 priority for me. It's not nice to sew on a table that shakes, rattles and rolls with your machine!
#2 priority is a flat working space. This is relatively easily (and inexpensively) achieved by creating a styrofoam surround for your machine. See these Youtube videos:
http://www.youtube.com/watch?v=g14go...ure=plpp_video
http://www.youtube.com/watch?v=yAS25...ure=plpp_video