Well, let's assume that all things are equal, ie such as source material has the re-issue been pressed using the original masters, or has it been re-cut using a cd as its source material, is the vinyl the record is actually made from of comparable quality etc etc.
In this case I'd say it depends entirely on the condition of the original. Some people will always go for an original release over a re-issue because they state that the quality of the pressing and therefore the sound quality is usually superior.
All things not being equal.... well then it's a toss up. Sorry, the only way is to suck it & see.
If it helps, I generally buy second hand vinyl as long as it's in excellent, near mint or mint condition. I've not had too many disasters, and even if a record is dodgy it usually only owes me a fiver or less. I've got a few "Nice Price" type re-issue pressings from the 80's which were, as the name suggests, cheap when they were released, and the quality on those is pretty acceptable/good if they've been looked after.
Occasionally I'll buy new re-issues if they're carefully done, like the current Pink Floyd re-issues (but I hardly ever buy them at full price.. amazing how much a crease on a cover can knock the price down).