Check the weight on each chair.  Most likely, the heavier chair is the one you will want to purchase.  Heavier bar stools are made with higher quality (i.e. thicker) steel tubing.  This is very important as light weight tubing is more likely to bend, and cannot hold welds as well.  Chair makers do not always tell you the steel tubing gauge.  The reason for this is because many times, they can cut costs if the raw material prices rise.  They can quietly keep the price the same by reducing the quality of raw materials.  This also makes it very hard to perform apples to apples comparisons with prospective commercial bar stools.

Avoid chairs with fabric or foam cushions for commercial environments.  Fabric chairs are prone to ripping and or staining.  This is especially true in a bar setting as the customers can often be very rowdy.  You do not want to have to continually replace or repair damaged fabric chairs.  Foam cushioned bar stools are also not a good choice in a bar environment.  Foam will wear out over time, and it is impractical to replace the foam on chairs.  If you do decide to purchase foam however, always check a sample in advance.  If you are purchasing a large number of chairs, you may want to purchase a single chair first in order to check the quality.  High density foam will last much longer.  You want foam which is firm to the touch (similar to the foam used in automobiles).