PHP overall. PHP can be used for everything you mentioned.
The login, register, member section are very easy to do - there are many, many resources on the web to help you out.
I would use Javascript and Ajax for the front end of the Channel Preference section (for being seamless - however make sure that if someone has javascript disabled it will still work)
Creating PDFs using PHP is not a fun task -
http://www.fpdf.org/ - that site is your best bet. From experience using it, it is very easy, but very tedious.
Any language can do math.
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PS: Should learn Python 2.7