I truly and deeply empathize with the OP. I have tried every GTD software application in existence (seriously, you name it and I have tried it) and they all have failed for a variety of reasons. Without going into a tremendously long story, I wound up on Emacs and created the ultimate GTD application on Emacs (no, it's not public ... yet?). It's all plain-text, which ultimately many people seem to also fall back on, as using databases, while nice, have a few inherent limitations: they are a binary format not easily changed, they require an application front-end to manipulate and interact with in any realistic fashion, and databases must have a rigid structure (i.e. a schema) that is tremendously difficult to change (without losing data) and therefore customize. They have a large number of benefits too but that is a whole other conversation.
In short, the reasons I chose Emacs came down to having complete control, and I do mean absolute, complete, unilateral control of every single aspect. Considering that it is already an x-plat software (i.e. works pretty much everywhere), it really makes the most sense. Couple that with the fact the Emacs' capabilities are/is the stuff of legend and the stability of Emacs as a piece of software (it has been in existence since 1975 and publicly since 1985 ... operating systems and tech companies don't even have that kind of heritage), there has been, and is, nothing else to challenge Emacs.
The single downside to Emacs is that it is not for the faint of heart when it comes to working with an old school "keyboard driven" application. Yes, you can use a mouse but Emacs is first-and-foremost a keyboard-centric application that demands users be not only touch typists but quite skilled with keyboard shortcuts and configuring everything. However, provided one does indeed master using a keyboard, they will experience truly boundless possibilities with Emacs.