Fabulous question!
Actually, I am/was a long time Omnifocus user, but am now on MLO (I do use Windows at work, so that factored into it of course). But after using MLO for about 6 months, and even trying other Web based services recently like Iqtell, Zendone, and Todoist, I have found nothing, I mean, nothing, that even comes close to the breath of functionality, speed, and usability of MLO. For almost every feature the other GTD apps lack, MLO has. I am in the process of writing a LONG post in the "why I like MLO" thread, that will explain this is in detail. Yeah, I would love for MLO to have a Mac, or probably better yet, Web UI version, but nonetheless, MLO is so good, it's woth virtualizing it on a Mac (or Linux) in some way (Crossovers, Parallels, VMware Fusion or Workstation). Unfortunately, that means additional $$ to spend on these hypervisors and/or a Windows license.
Aaron, keep an eye out in the pinned thread about "Why I like MLO" for more details.
-Brian