Magnum Opus or MMM?
 

Looking at the date, Magnum Opus was last "updated" on Jan 2011 which is more than a year now whereas the MMM was "updated" on March 2012.

Is it still worth getting Magnum Opus? Will it work with MMM? Or should I just get MMM?

Maybe You can try MMM and if You don't like it try MO.

Personally I use AIO 0.5 MMM now and it seems to be working very well but the choice is Yours, ofcourse...

If You install MMM I suggest You read very carefulle page 1 instructions.

I was just looking, and MMM has everything I want, plus a whole lot more. I do not think my old girl could handle all that. MO seems like a balanced package that won't have my comp melt, heh. Its just that MO has not been updated in awhile. I am going to try MMM, lets see how it runs, does not hurt to try.

I've not "looked" into both as I'm just following Stoianm's mod recommendation and his #2 on the tutorial is the Magnum Opus mod. What does one have that the other has not?

From what I understand, MMM is just a "collection" of mods that have been proven to work together, right? Is MO the same?

Yes - they are. Read instruction of the both mods and You can see about what they are...