Currently on paper
I too use a paper system. I too have gone back and forth. As it stands right now, I am solely on paper. I found that the temptation to leave old copies of lists in digital format was just too strong, especially when storage is so cheap and text files are so small. For instance, when transferring to my USB key, I would not delete the old copies on my hard drive (fear of losing key). Then, I would copy those lists to a laptop or other machine from the key. I would probably delete from the laptop when done, but then I have to reconcile the changes with my original lists on the hard drive once the changes came back in. If I took the time to use a naming convention and archive older versions, etc., it would feel too much like drag on my system. Even when cleaning out old "reference" (i.e. deleting old archived versions and folders on hard drive), I would be strongly compelled to do that one last look over every copy just in case I missed that one special list item. Again, too much drag.
Now, the ONE THING I LOVE about digital is the ability to delete a friggin' line when done! On paper, old tasks are crossed out and then when sheets get crowded and noisy, I eventually have to do the obligatory transfer of remaining tasks to a new sheet. To me, this is currently the lesser of two evils.
For repeat tasks, I use my Tickler File to remind me. I would really like some feedback on this approach. I couldn't bear cluttering email or calendar with so many task and event reminders, but I needed a way to do this function. So, the calendar is for known hard dates with certain people at certain times, but I use the Tickler File for day-specific reminders for events with no action yet decided about them, like birthdays and anniversaries. Example: For anniversary on October 31, I put note in "October" folder. Then I put "Call Restaurant xxxxx" on my @PHONE or @CALLS list, or a hard date on my calendar for that call, after I've dumped my tickler file into "IN" on the night before October 01. Putting "Anniversary" on my calendar is too ambiguous because there's work still to be defined for it.
One last tip I use is to put a label on each sheet of my lists. When I do that, I know that only papers with a label on them at the top are my canonical lists, and all the rest are scrap or working papers, or other. I do this because my loose-leaf binder has lots of other pages in it too, like reference and checklists.