Interesting question. With literally hundreds of pens to choose from, my grail pen tends to be the one I am working with at the time, and that can vary from an inexpensive Knox nib with a brass barrel, to my GvFC (which currently is my high-end). To me, the issue is what is the best writing nib. I have hoisted multithousand dollar pens that did not write well, while I have dozens of Knox nibs that are workhorses. Never a nick, nip, skip, or ooze. I have a Parker that needs regular encouragement and Levenger's that flow from full to empty with almost the same amount of coverage throughout.
In many cases, I have found that, more and more, I am becoming more of a paper snob than I am a pen snob. I like good pens, don't get me wrong, but good paper makes a marginal pen great in most cases.
Across the top is the Vanishing Point (Stormtrooper), bottom right, Knox (from Birmingham Pens), In the middle my Graf von Faber-Castell, and on the end a new one called Penlux (an aluminum body) that I just acquired.