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 ?
I echo most sentiments here. Tick, pops, surface noise or not on original pressings, once the music kicks in the magic begins. With a great majority of reissues, the drive to make a buck on the vinyl revival is obvious - there is no care for the sound quality. Awful vinyl quality, warps, off-center pressings, digital recording and mastering process rendering the record lifeless are the norm in today's offerings. There are exceptions but they are far and few between. My short list is as follows:
- Blue Note "Music Matters" The Definitive 45 Reissue Series. Absolutely flawless. Expensive, but insanely good, and worth every penny.
- Select Mobile Fidelity offerings. These can be hit or miss, but many are tremendous. A few favorites to mention from my collection: Carole King "The Carnegie Hall Concert," Rickie Lee Jones "Pirates," Art Pepper "The Way it Was," McCoy Tyner "Sahara."
- Select Speakers Corner releases. Supertramp "Crime of the Century" is outstanding.

To sum up, my advice would be to seek out original pressings first, and then very judiciously settle for reissues.
I agree with the OP, most of the reissues I've purchased were superior to the original. Most times it's just a matter of the sound being cleaned up, not changed or altered.
Your mention of the Stockfisch label is accurate IMO and I'm often surprised how little attention they get. The selection is limited and proprietary but I've always thought their releases sound very good to great. More Sara K and Chris Jones releases from them would be essentials on my list.
Viridian makes a good point about the condition of the master tape. Even if stored immaculately it will have degraded over years and decades.

I go for the original, pressed in the country in which the recording was made. There is a feedback process called the 'test pressing', that occurs between the artist and the record label. It only seems to occur in the country of origin. Working duplicate tapes of the master are generally shipped overseas for release in other countries. So the country of origin will usually have the sound that the artist approved (not saying in all cases that that is the best sound, but simply the one approved).

In this age of digital and limited LP releases, there are less differences between the countries if they are all working from the same digital master.

One thing that was a problem for some releases in the 60s was the issue of mono. There was a product designed so that the record labels could produce a single stereo LP that would also play properly in mono; this was so they did not have to do both mono and stereo releases. This product (Haeco CGS) was a processor that messed with phase, which muddies center channel information.

So if the reissue lacks that processing, it may well be that the reissue can sound quite a lot better.

Acoustic Sounds has done quite a lot of work with their pressing machines which are considerably more still during the pressing process. This makes for quieter vinyl. We have been cutting LPs, some of them reissues, where it appears that we are able to turn out masters better than the original. We are using a modified form of our M-60 amplifier for the cutting operation. IOW there are still advances being made in the LP process. If, during the mastering process, you have a good master tape and the original LP in front of you, I would say that there is opportunity to have reissues that can sound better than the original. You just have to listen and see :)