This article is from the Fencing FAQ, by Morgan Burke with numerous contributions by others.
There are a large number of variables to consider when shopping
for blades, including stiffness, length, durability, flex point,
weight, balance, corrosion resistance, and (of course) price.
Stiff blades provide better point control, but less
"flickability". Some brands of blades (eg. Allstar) are sold in
different flexibility grades. Blades that feel heavy in the tip
often provide better point control, while those that are light in
the tip often make for faster parries.
Blades generally come in 5 sizes, 5 being the longest (90 cm for
foil and epee, not including tang) and by far the most common.
Shorter blades are somewhat lighter and quicker of action, and
can be useful for children, fencers who prefer the lighter
balance, or those who often provoke infighting in which a long
blade can be disadvantageous.
Cheap blades (including some Eastern European and Chinese brands)
are typically not very durable or of poor temper, being inclined
to snap, bend, and rust easily. Fencers who are gentle with
their blades and clean, sand, or oil them regularly may
nevertheless find them to be a good value.
Blades typically break at the flex point in the foible. Less
commonly the tips will break off, or the tang will snap at the
base of the blade (this latter failure mode is fairly common in
sabre). Other serious modes of failure include sharp bends in
the middle of the blade and S-bends in the foible, both of which
are difficult to remove and will rapidly lead to fatiguing and
eventual breaking of the blade.