One nice thing about refills is that it gets you into a much nicer class of pen body - it's amazing how much difference a nice texture and better weight and balance can make. Of course, then you need to be careful to not lose them!
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.
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.
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.