I've given up chasing the software solution and realised that a paper to do list (managed in a Filofax) is the optimal for me. Most of my tasks come my way through face to face discussion so there's no email to convert to a task etc. And if it can't be taken off the list this week then it's probably a project that needs diarying.
I do use Outlook for diary management but that's because I work in a corporate environment and trying to do anything else would be working against the system. But it's one calendar for everything (work and personal).
Paper works for me, too. I get intense cathartic satisfaction in drawing my checkboxes (with drop shadows)--my co-workers make fun of me.* There's value in not only having a to-do list, but re-writing it from time-to-time.
I've tried multiple software applications, from plain text, to trello, to custom software. Nothing works as well.
* This actually serves another purpose as well: in a page full of notes, my drop-shadowed action items pop out.
I do use Outlook for diary management but that's because I work in a corporate environment and trying to do anything else would be working against the system. But it's one calendar for everything (work and personal).