My questions:
(1) What is West System? Is is a Polyester resin, a Vinyl ester resin,
or an Epoxy resin fiberglass repair solution?.

WEST, which at least originally stood for something like Woode Epoxy Saturation
Technique, is an epoxy. While it may originally have been formulated for
coating and bonding wood, it is also used for layup of glass, Kevlar, carbon
fiber. The salesmen would probably call it a "system" as they have several
hardners, and perhaps more than one base resin, as well as a range of additives
that can be used to change the properties of the resin (eg. Colloidal silica
a.k.a cabosil is a great thickner for epoxy when you want a bonding paste, or
for thickening epoxy so it won't run for small repairs, while microballons are
great for making a low density paste that is easily sanded, for fairing).

Alternatives to WEST would be epoxies from companies like SP Systems, MAS,
System 3. None of which I have any first hand experience with.

Vinylester is sort of between polyester and epoxy in both properties and cost.
Vinylester is typically quite a bit better than polyester, but not as good as
epoxy. But I should include caveats like "it depends what you are doing"

How do these compare? I
am over simplifying the options?

(2) I have heard a lot recently about Vinyl esters as having good
properties. What are its pros and cons. If this is not what West
System is, from the experts, how does it compare?. Any reputable
suppliers?

Components of high performance (eg. fighter) aircraft would likely be pre-preg
carbon-with-epoxy.

Very high performance sailboats where strength and stiffness are very important
would probably go with wet layup, vacuum-bagged carbon, Kevlar and epoxy.

Apparently lots of offshore racing powerboats are built with vinylester. I
would guess some use epoxy too.

Most recreational not-super-high-performance sailboats are polyester. Some
kep-in-the-water boats use a layer of vinylester to prevent the underlying
polyester being eposed to water, as it tends to slowly absorb water. Certainly
some boats, probably more expensive than typical, but not where ultimate
strength and stiffness were appropriate, would be built completely of
vinylester.

Boats that are mostly glass cloth are frequently built using polyester or
vinylester. To get maximum benefit from Kevlar and carbon fiber, builders
would typically use epoxy in boats using significant amounts of carbon and
Kevlar.

Alexander "Ali" Meller
http://www.sailing.org/int505/