in reality the differences will be hard to determine on a bottom rung big name bike vs a average box retailer. honestly they are all made in taiwan/china and the parts although have the shimano name will also be sourced from a third party company. i would say go for the bike that fits better and is the more comfortable ride. if it sucks to ride you will never ride it and therefore you may never get into biking and this will be all moot. good thing about walmart is that although you cannot test ride it before you buy, you can return it for full refund (make sure you keep all tags and dont remove stickers) within a few days. i doubt a local bike shop will be so understanding. just take it home, ride it around the neighborhood, then when you get the feel go find the most difficult part of your commute and see how it fares.