For weight less than the 60lb mark, I would suggest the powerblocks. Ive spent several days reading reviews and heading out to stores to test all of them...and while I love the look of the bowflex, the powerblocks were much more sturdy, smaller etc...everything that you read in reviews online.
Another thing of note...every store I went to I asked the people working what they thought of the two and they all said the same thing: lots of their patrons have had problems with the bowflex (gear issues, rattly weights, etc.) and no complaints about the powerblocks.
Who knows. Check this out as well for a size comparison etc. If you are doing bicep curls, those bowflex are oftly wide to be holding two...
http://www.powerblock.com/competition.html