Ubuntu (Free) is the most popular version of Linux, so the translation is that it probably has the most support (more likely your canon printer will work).
I've been using it for several years now, & find it very stable & extremely secure, you don't need an antivirus program for Linux (security programs won't slow down your OS). As you can see it's vulnerabilities are 100% patched one hundred percent of the time
http://secunia.com/advisories/product/32688/
Whereas Windows & Mac have unpatched vulnerabilities 100% of the time, hence the need for antivirus programs
http://secunia.com/advisories/product/27467/
http://secunia.com/advisories/product/96/?task=advisories
According to this site, mathematica will work on Ubuntu
http://www.wolfram.com/mathematica/features/system-requirements.html
Or maybe you could use a mathematica equivalent
http://ubuntuforums.org/showthread.php?t=489196
Apparently, BSNL Broadband will work in the newest versions of Ubuntu
http://askubuntu.com/questions/24285/connecting-with-a-bsnl-broadband-internet
Watching moves shouldn't be a problem, you may have to install a few extra codecs though, there are two commands for this that you will need to run in the terminal (perhaps the only time you will ever need to run any commands)
https://help.ubuntu.com/community/RestrictedFormats/PlayingDVDs
Other than running the 2 commands to watch DVDs, you normally just install software the easy way by using the Software Center
http://www.youtube.com/watch?v=G5ZpspkfbDg
You should wait two more days to download Ubuntu because the latest version will come out on April 28