Do a Google search on each followed by the word "reviews" to get more opinions. Here is the first website I found that way:
http://elizabethruffing.com/2010/05/...e-lowdown.html
I haven't done this on both machines and read all the reviews, but my gut feeling is that the Sweet Sixteen is a better bet. This is in part because I have seen a lot of posts about the SS and few about the Viking, plus all the ones about the SS that I have seen have been positive. My bet is that the SS has been around longer and is better known. Being better known means it is easier to sell later if you ever want to upgrade.