I mostly use my Traveler's Company brass fountain pen fitted with a Schmidt EF nib because It's always with me attached to my Traveler's Notebook. My backup 2nd most used was YStudio's Brassing Portable which I ended up losing while traveling in Italy's Adriatic coast. I typically cary 2 pens with different colours. In the Traveler's Company pen I use Diamine's Writer's blood and in the YStudio, I was using Diamine's Hell's Bells. Having 2 pens with two inks enables me to have more flexibility in contextual jotting.

My EDC is made of three fountain pens:

• Lamy Safari (ef nib, De Atramentis Document Brown ink). I use this one for sketching (waterproof ink works great with watercolors). But a Safari has been part of my EDC since the very early 00s I like them a lot.
• Around 2010/2015, I started using Twsbi, another great fp. Nowadays I carry one for their Twsbi Eco (ef, Pilot Kon-Peki blue ink) for its ginormous ink capacity. I also like its look.
• Very recently, like half a year at most, I started using a Platinum Preppy (ef, Platinum Carbon Black ink) and I must say I'm really impressed by it. Very cheap, nice (steel) nib and sturdy. Its look is the most... forgettable of the three fountain pens, but I'm fine with that, even more that, being Japanese made, they sport a finer nib than Lamy and even Twsbi who both use German/larger nibs ;)

They're all good writers and they're not expensive (Preppy being the cheapest, by far). So, I can enjoy a fine writing experience without worrying about damaging my more expensive fountain pens.

I have a bottle of writers blood too. It's a great colour!

Where are you from? Is diamine expensive ink where you are? I'm in the UK and I'm always surprised how cheap it is to buy.