Personally, my third piece of the "trifecta" is Personal Kanban. It's has some huge strengths and some small problems, just like the other two. It is inherently visual, which is a huge plus for me, but it's kinda hard to fit all of your items on any board, so I don't use it to put my entire task list onto, because that wouldn't work. Here are a few ways I use it:
A visual representation of the week ahead, so I can move things around and when they're done, they go to the done column
If there's some important project I'm working on, I'll have the board for that project
I use it to hold ideas as well, but that is kind of being migrated over to evenote, which by the way is a great way to implement GTD.
There is a great blog post on using Trello (which I've talked about before) for GTD, which since you're using trello, you're kind of using Personal Kanban as well.
I would also strongly recommend Kanbanflow if you're looking to impliment Pomodoro Technique, GTD, and maybe Kanban, as it has a Pomodoro timer built in, and also records the amount of time spent on each task, which is super awesome. There's just so many different apps that I jump between I've told myself I have to stop and I've settled with doit.im since I paid for a year of premium, but knowing how much time you're spending on each task is a huge positive aspect of kanbanflow. I hope this helps.