I've been on the hunt for the "perfect" body for years after having gone way too in depth into testing refills and obsessing over minutiae of the writing experience, but I seem to want the opposite of what most people do. I want the perfect "cheap" capped body for a Pilot G2 1.0mm refill. I've tried all the other equivalent refills and this is my jam. The closest body I have found is the Energel Deluxe capped body, but it requires modification that often breaks the tip opening so that a Pilot refill can fit through it since it annoyingly has a larger tip on the 1.0mm than the other compatible refills like Energel, Sarasa etc. Pilot doesn't make a refillable capped body like this. I don't like the heavy or metal fancy pen bodies most people are drawn too, which is good for me as they cost too much anyway and I don't have disposable income, but it's one of those little annoying first world issues in life I wish I could solve. My perfect body would be a clear demonstrator type capped body (easy to see ink level and color) of the diameter I like, with a decent grip material. Really the Energel above, clear, with the proper tip for the G2, and a better clip, would be 90% there for me. Small problems.
I also habitually carry fountain pens, a ball point or gel pen, and a mechanical pencil (Pentel Graphgear 1000). My EDC fountain pens typically includes a Visconti Homo Sapiens Maxi Bronze Age, Pelikan Souverän M805 Ocean Swirl, and a Lamy 2000 (inked with Montblanc Oyster Grey) in a leather pen case. I also carry a Kaweco Liliput with a Monteverde green refill when I'm traveling and it is impractical to carry/use my pen case.
The vast majority of my writing, however, is in fountain pen. It may not be as convinient as a ball point or gell pen, but the writing experience is just far better--especially for more expensive fountain pens.
I'm mostly using a Super5 fountain pen, about on par with a Lamy Safari, with Monteverde blue-black ink. Totally agree on the writing experience... a fountain pen just feels so much better than any ball-type or felt-type pen. So my EDC is just the Super5 and a Uni-Ball Jetstream (mostly for receipts), but I really should carry another pen as a sacrificial "Hey, do you have a pen I can borrow?"
I also like the Hi-Tec-C refills. I wanted to use them with a pen that takes a (IIRC) Parker style refill so I used a 3d-printer to print an adapter I slide over the refill.
That's a good idea. I want something so I can just buy cheap Hi-Tec-C pens by the box, and use them in an actual nice body.
I habitually carry multiple pens - at very least, a fountain pen and a disposable ballpoint that I like (Uni-Ball Jetstream). The ballpoint is for signing receipts mostly, so I don't have to use whatever they give me, and for loaning to people who suddenly need a pen. I assume I'll never get it back when that happens.
I sometimes carry a fine Sharpie as well, for things where I want a wider line on whatever sorts of surfaces. And if I'm really swinging, I'll have other disposables.
For a while, I was carrying a Retro51 Tornado (beautiful and affordable) with a Monteverde blue-black gel refill that is maybe the nicest-looking ink I've found. But it's a bit broader than I like, and they don't make a finer point.
I also really love the Pilot Hi-Tec-C, but unfortunately, they don't really make proper refills for it, and the disposable bodies are trash, to put it nicely. Absolutely the best fine-line disposable writing experience, though.