My most regularly used #fountainpens, in order of regularity of use:

1. Kaweco Liliput, copper, extra fine steel nib
2. Pilot Lady, extra fine gold nib
3. Pilot Custom Heritage 912, FA nib, aftermarket ebonite feed

The Kaweco will go months without drying out and can live in my jeans pocket. The 912 is big and thirsty and that's why I'll more often grab the Lady for longer writing sessions.

@vwbusguy Do you use a cartridge or converter in the Kaweco? I got a Kaweco AL Sport and planned to use it as a pocket pen. Unfortunately, twice the converter came loose from the feed while I was carrying it and leaked ink into the barrel. I stopped carrying it after the second time.
@vwbusguy I also have a Liliput as an EDC pocket pen.
@WordChuck I use only cartridges. The normal Kaweco Sport mini-converter doesn't fit in the Liliput. They used to make a bespoke squeeze converter for the Liliput, but I haven't been able to source it for more than a year now, and it's no longer lister on their site.
My cartridge of choice for my Liliput is Montblanc Permanent Blue.
@jeffweiss @vwbusguy Ah, ok thanks. I’m not really familiar with the Lilliput other than the name.
@WordChuck @vwbusguy here are a couple comparison photos of the Liliput and AL Sport.

@jeffweiss @WordChuck Yup. It's also possible to refill old cartridges using a blunt syringe and any bottled *fountain pen* (not dip pen!) ink you want. Fill the syringe with water and inject it in to clean the cartridge out between ink brand/color changes. Blunt syringes are only a couple of dollars and Goulet sells them if you want to buy one from a #fountainpen retailer.

https://www.gouletpens.com/collections/pen-cleaning-supplies/products/goulet-5ml-ink-syringes#

Goulet 5ml Ink Syringes (Set of 2)

@WordChuck The Sport and Liliput are both too small for converters, IIRC, but I have a Perkeo that I use a standard international converter on. You can use any standard international mini cartridges in a Kaweco as they use Bock or Jowo nibs and feeds. Generally, converters should never come loose in a pen, but I don't believe the sport or Liliput were designed to accept converters.