While I certainly like fountain pens, I also like other types of writing instruments and use them as well.
I prefer a Western XF nib on a fountain pen. With Japanese nibs, I prefer a F or even Fine-Medium (I have a Pilot Custom 74 with a F-M nib and it's very nice.)
I like and use the Pentel Philography pen, but with Uniball Signo 0.5 refills.
I also like the Uniball Jetstream pens for some uses, and the 0.7mm is the width I prefer. I've found that the thinner widths don't put don't put down enough ink to have as dark a line as I like.
I've tried a lot of mechanical pencils, but the first 0.5mm pencil I ever bought, a Pentel P205, is what I keep coming back to. I've bought other P205s since then, as well as the P207 and P209, but I still have the first one on my desk at home and use it.
I also like the Parker Jotter pen. I had some Itoya GPR-7 refills that I liked a lot, but they either stopped making them or stopped importing them. I've tried some other refills instead, like the Schneider Gelion 39, but they don't work as well for me as the Itoya ones did. (I can still get the Itoya AQR Aquaroller refills, but I don't like those.)
Finally, if I need a pen that I don't mind losing or having damaged, I use the BIC pens with the Ultra ink. Only the Ultra Stic models seems to have this. They don't write as well as the Uni Jetstream, but they're much less expensive.