Some good and some really poor advice here.
First off, the MTT or STT question makes a world of difference. Also, if you find yourself constantly (regularly) being SS - or even simply going out - before or on the bubble, then you need to look at why this is first.
Other than that, it is always gonna be situation dependent.
As already said by another, this post:
"It depends on a number of different things. Your cards, stack size, your opponents stack size, your position and how your opponents are playing. The best thing to do is to post your hand histories of spots you are having trouble with and people here will give you there advise on what you should do."
kinda says it all.