How to decide what to buy digitally?

Ok, so this has been bugging me for a while but how do I decide what comic books I should buy digitally?

Now, don't get me wrong, I enjoy digital and print comics in equal measure, but how my pull list is divided between them is not so equal, with print getting the lion's share. This, of course, becomes a problem as print issues take up a lot more space. I've got seven short boxes and two long boxes, along with three shelves of trades throughout my home (not to mention the tonne of physical books, dvd's and video games, but that's a conversation for another time).

So, I ask this question because I figure, maybe it's time I started to readdress the balance between print and digital and save myself some space. That said, how do I choose what to buy digitally and what to buy as print?

In order to decide this, it's probably best to show what the current split looks like. When I buy digitally, books consist of Alex + Ada, Dead Body Road and Serenity: Leaves on the Wind. With Print however, the books are Earth 2, Fantastic Four, Daredevil, She-Hulk, Lazarus and Mass Effect: Foundations.

Based on those lists, print books consist of (mostly) ongoing series while digital are made up of limited series. This, I think is a good way to differentiate as Ongoing series could be considered more collectable while, at the same time, if I had 50 issues of Daredevil on my Ipad (my primary source of digital comic reading), then a) disk space would be all gone and b) my OCD would go crazy at having so much on my Ipad.

Of course, it becomes an problem when I pick up an ongoing series that ends up finishing after, say, 12 issues. Uncanny X-Force (Remender's run) was terrific and I got every issue. However, if I'd known it would have ended at issue 30 then I would have considered getting the whole thing digitally. Hindsight is a wonderful thing.

This month I'm picking up issue 1's of Secret Origins, Iron Fist and Inhuman. I'm highly suspicious that none of these will last past 30 issues and am tempted to digitally pick up either Inhuman or Secret Origins. However, if by some miracle that were to happen, then the above problems for me would kick in, which I don't really want to face (though maybe I should).

Maybe I should stick with the division method I currently have in place; ongoings in print, limiteds by digital. However, with less limited series making my list that is becoming very skewed against digital and that's not what I want. I want to lessen the burden on the space in my house, which means digital is the way forward. I want to balance out my collection between the long box and the memory box, I just need a new criteria with which to distinguish between them.

If anyone who reads this can give me a suggestion, I'm all ears.