When using a plastic carboy as a secondary or for storage it should ONLY be the type that are marked PETE (or PET) ... this is to avoid chemicals leaching into the wine from the plastic.
This designation is found on the bottom of the carboy or jug with the word PETE or PET under a little triangle made of arrows with the number "1" in the triangle. (example on this page ... http://en.wikipedia.org/wiki/Resin_identification_code
These PETE carboys can include various ones from brewers/vinters stores, Absopure and elsewhere.
When it comes to storing wine etc, the closure (the airlock or stopper) is particularly important. The closure is much more likely to allow unwanted oxygen than the carboy itself.
Here's some info on a specialty closure system .. the Better Bottles system which includes the carboy and closure. This is a particularly good system for longer term storage.
Info at ...
Better Bottles has an informative website as well.