Choosing between Reissue and Original pressings


Reissues have been common since quite some time but these days as vinyl has picked up momentum again, there have been some very high quality reissues from labels like Classic, Analogue Productions, Speakers corner, MFSL, Boxstar etc. For any particular album how do you decide whether buy a good reissue or get a good copy of original pressing from ebay ?

For the sake of discussion lets keep out exceptions where the original pressing is too hard to get or too expensive. In most cases it is possible to buy a copy of original pressing for sane amount of money if one shops carefully on ebay but I have also found that quite a few times a high quality reissue can sound better. Whats the general thought among hardcore vinyl followers here ?
pani
Ralph: any way to discern which records used the Haeco CGS process?
Are they early stereos that had the legend that said something "fully compatible on mono players, but for best results, play on a Stereo"?
Is your last line a tease?
Working duplicate tapes of the master are generally shipped overseas for release in other countries.

These duplicate copies were most probably made out of the original copy ? If yes then obviously they would be inferior to the original because in analog there is always loss when transferring information from one tape to another! So, probably the tape that were being used in other countries were inferior in the first place ?
In the industry they are referred to as "safety masters". As in assuring that the nit wits in the country that I am shipping this tape to will not have the opportunity to ravage the master tape.

They are generally made from the master or a couple generations removed from that. Unfortunately, the record business has been a bit of a seat-of-the-pants enterprise and a substantial amount of the masters of our musical heritage have simply been lost, mis-filed, or severely degraded due to volitile tape formulations, or incorrect storage.

In those cases, safety masters may be the best extant masters. And worse, in some cases, all tapes have been lost.

My copy of Mosaic's "The Complete Pacific Jazz Chet Baker/Russ Freeman" is actually recorded from vinyl records played back as some of the masters were lost. Even more embarrasing, my original 10" Chet/Russ recordings are in better shape than the ones that they used to make the records. Go figgur!
Viridian, It's ironic but it looks like vinyl will turn out to be the longest lasting medium for archiving music. With minimal efforts at storage, a vinyl record can maintain its sound quality indefinitely and even if there is some defect the problem rarely results in not being able to hear the music. The same can not be said of tape or any form of digital storage.
Whart, if you see that, then yes. You might want to read the Wikipedia page on the Heaco.http://en.wikipedia.org/wiki/Haeco-CSG

Pani, correct. That is why the country of origin is so important. ELP released their first LP in the US and the UK. The US Cotillion is quite good, but the Pink Island is much more lively...