Generally speaking larger drives are a more efficient way to buy storage volume.
I buy my drives based on the price/gb
Currently I have a pair of 1.5Tb drives for audio (and some recorded concerts)
and another pair of 3tb drives plus a 2tb external for Recorded TV programs and movies.
One decision you need to make is what container format to use.
While some will tell you that MKV files are the most efficient use of space
I adopted mp4 as my file format of choice.
Not that there's anything wrong with MKV files... both my large format TV's will play MKV files directly, but I adopted mp4 for computer based playback before the MKV file form was available.
Windows7 computers will playback mp4 natively
I've had issues with some MKV files on different computers.
what was the solution to that problem? Well I probably didn't employ the most elegant solution, what I did was convert the offending files to mp4.
I already knew how to do that....
Like most people I do things the way I'm used to doing them...