Gondola Shelving BrandsThe brand name of your shelving should be a consideration in many situations.

Will parts be available later?
Will you want to add on a few matching section someday?  Is the manufacturer still in business?
Do the current parts integrate with old parts?

Gondola Shelving Manufacturers:

Lozier (website)
Madix (website)
Kent (website)
M.E.G. (website)
Streater (website)
Handy (website)
L.A. Darling (website)
StorFlex (website)
Canada's Best (website)
Wilson Display (website)
Hussman (website)
O.S.F. (out of business)
Lozier - The most prominent used shelving in the USA is Lozier, Madix would be a distant second.
Im not saying Lozier is better than Kent, Madix or O.S.F., I'm just saying there is more of it (used) out there.

It's been a popular brand of shelving for a long time.  (Many) Lozier gondola parts can be interchange from different manufacturing dates. A Lozier base bracket made in 1968 might fit with a lozier upright made in 1995.
In terms of the used market, this has a huge impact on the ability of dealers to piece together complete stores, thus recycling more used Lozier back into the world.

Once in a while, when a shelving dealer liquidates a local store, they have a leftover pallet of shelving parts(sometimes new in box, often over-ordered from the closing store). Dealers might simply scrap a pallet of odd O.S.F. uprights or base brackets, but they would rarely dump Lozier parts...they can use those with other, readily available, Lozier parts to make and sell complete units.

Madix - The merger of Dixie Craft Manufacturing and Maytex Store Fixtures formed Madix, Inc. in 1982. 
Dixie Craft Manufacturing was founded in 1956, the same year as Lozier, but the current shelving recipe of Madix began in the 80's (to the best of my knowledge).

This might explain why there's more 40 year old Lozier uprights and shelves floating around the market and bearing loads in stores today.  The Madix that is floating around (there's plenty) should be, therefore, have less wear.

Madix is very similar to Lozier.  They look similiar; both the completed units and many of the parts.  They are both high quality products, still manufacturered and available today in the United States.  Both maintain a solid level of backward compatibilty with their older maufacturing dates.