All of these fit the standard Pilot G2–style retractable refill, so you can put pretty much any ink and width in them, including my current pick for black, the Uni-Ball One.
My current favorite gel pen body is the Sarasa Grand. They’re made of brass, which gives them a solid heft. I go with the standard ones, rather than the Vintage, just because I’m not a fan of gold tones on the clips. (Though the bordeaux purple body is quite appealing.)
Typically these come with 0.7mm refills that I toss immediately for being too wide. Sarasa also isn’t high on my list of gel inks anyway.
I’m a sucker for the retro-ish stylings of these. Good click action, too.
These are metal, which I like, but they’re not nearly as heavy as the Sarasa Grand, which is too bad. I like that they come in purple.
They’re notable, however, for having an incredibly chonky click to them. It’s got a lot of recoil. It’s fun.