This article is from the Model Trains FAQ, by Christopher D Coleman with numerous contributions by others.
Most starter sets come with O-27 track as a purely economical
measure. It is expected that you will buy better track if you
more than double the size of your layout. Here's some deciding
factors:
Reliability
O-27 - the physically weakest of the systems. Stepping on a
section will seriously damage it. About 50 pounds of pressure
will throw it out of alignment.
O - Much stronger, takes a lickin and keeps on trackin. Joint to
not wear as fast as O-27.
Super-O - Pretty strong, but does not tolerate constant
dissassembly and reassembly well. Snap together fingers and pins
are more likely to snap.
GarGraves - Moderately strong. Ties will crack and rail will fold
under 100 punds or so. Rails are attached to ties by tention of
the rail against the pocket in the tie.
Realism
O-27 - Low. More realsitic than O. Since 1971 has had brown ties
rather than black. More realistic rail height.
Will accept only flat additional ties. Curves range from absurdly
tight to plausible.
O - Low. Least realistic, large, wide black ties and very tall
rail. Will accept more 'squarish' additional ties than
O-27. Curves range from absurdly tight to plausible.
Super-O - Excelent. Very relistic plastic molded details
including spike heads and tie plates, but ties are unrealisticly
sloped. Flat copper center rail is less visible. No need for
additional ties. Curves are semi-absurd tightness.
Gar-Graves - Excellent. Quite realistc, stained real wood
ties. Blackened center rail is much less visible. Curves can be
to scale.
Economy
O-27 - Cheap. About a buck per new section.
O - Inexpensive. About $1.50 per section.
Super O - Expensive. Has not been produced for many years and
pieces are collectable.
Gargraves - Intermediate. About $4 for 3' section.
Variety
O-27 - Lots. Comes in several curve diamaters and all forms of
special track sections.
O - Much. Comes in several curve diameters and most forms of
special track sections.
Super-O - Few. Singe curve diameter and moderate number of
special track sections.
GarGraves - Infinite. Curves down to 36" are possible. Switches
avalable but most other special sections must be customized.
Compatibility
O-27 - 27" curves and switches will not accomodate larger "O
Scale" equipment. Older Marx is incampatible with Lionel switches
and vice versa.
O - 31" curves and switches will not accomodate larger "O Scale"
equipment. Older Marx is incampatible with Lionel switches and
vice versa.
Super-O - Will accomodate up to medium-large equipment.
GarGraves - Can accomodate nearly any equipment.
Kid Play Value
O-27 - Good. Easily changed into varied and complex layouts.
O - Excelent. Easily changed into varied and complex
layouts. Strong.
Super-O - Moderate. Less flexibility in design, less resistance
to play.
GarGraves - Low. Once flexed, cannot be flexed again.
 
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