I want to use NumPy/SciPy. Should I use Python 2 or 3?
I can recommend Using py3k over py2.6 if possible. Especially if you're a new user, since some of the syntax changes in py3k and it'll be harder to get used the new syntax if you're starting out learning the old.
The modules you mention all have support for py3k but as SilentGhost noted you might want to check for compatibility with plotting libraries too.
I am about to embark on some signal processing work using NumPy/SciPy. However, I have never used Python before and don't know where to start.
I see there are currently two branches of Python in this world: Version 2.x and 3.x. 
Being a neophile, I instinctively tend to go for the newer one, but there seems to be a lot of talk about incompatibilities between the two. Numpy seems to be compatible with Python 3. I can't find any documents on SciPy.
Would you recommend to go with Python 3 or 2?
(could you point me to some resources to get started? I know C/C++, Ruby, Matlab and some other stuff and basically want to use NumPy instead of Matlab.)