I also strongly recommend using an iron gall ink (Platinum makes a few; another very good one is http://www.registrarsink.co.uk). Those inks are very easy to work with, even on the crappiest paper, and are quite resistant to UV, water, and other hasards.
I have a small collection of fountain pens and have bought and sold many others. I have found that much of this is personal taste and how you use it. Some pens feel comfortable in the hand. Different pens sizes (length and diameter), shapes, and weights will feel good to different people. Some prefer to post the cap on the end of the pen while writing. Others prefer not doing that. Doing it affects balances differently for different pens.
There are also a wide variety of nibs to choose from. They can vary in material, widths, firmness, and how they flow across different papers. If you mostly like a nib, but it's still not quite right for you, you can have a nibmeister tune it more to your liking.
Some who write a great deal are not comfortable with the smaller quantity of ink in a cartridge converter or the shorter refill cartridges. I have used pens with these and still have some, but prefer a piston filler for the usually larger quantity of ink it can hold. It is even better (for me) when I can also look at it and see how much ink remains. But, if you have those and then rarely use it, ink can dry in the feed. In that case, something with an ink cut-off, like the Pilot Custom 823 Amber, may let the majority of ink remain even if not used. That pen is one of my favorites.
You can try any pen as a starter. But, if you don't like it, remember the preferences. That pen may not suit you, but another may be a perfect fit. Welcome to the hunt for the perfect pen.
You'll get plenty of suggestions for places to start, let me suggest the Pilot Vanishing Point as something to aspire to.
It's a real pleasure to look at, carry, and use, but it's too nice to be the pen that lets you discover that fountain pens aren't for you. It's ok if they aren't, they really aren't for everybody. As a daily driver I highly recommend it.
For your first experiment with them? I would go with a pilot varsity. It is a disposable fountain pen. They cost a couple of bucks each, so it is cheap enough to make it an impulse buy or a regular buy if like me you lose your pens regularly.
Another option at the impulse buy level is pilot Petit1, it is a short pen you can throw in a pocket. It is refillable, not disposable.
I'm not a collector but got myself a couple during the pandemic. Pilot Metropolitan has good reviews and I like it a lot. It's a starter pen from a well-known company and is under $50 on Amazon. I use cartridges pre-filled with ink but also have a refillable container when I run out.
I also have one of the Chinese clones of infamous Parker 45, with refillable container. It works pretty well too but I like Pilot better.
I find that writing in cursive helps me clear my thoughts, think things through, calm down, almost like meditation. It's pretty cool.
There's also a subreddit for fans, with an obvious name.
Someone already mentioned the Lamy Safari which I think is a great starter pen but the Pilot Metropolitan, Kaweco sport, and TWSBI Eco are all great. I think the last one is kind of ugly but I have one and it writes well.
Others have already mentioned good pens to start with, but I want to mention that the paper is equally important. Clairefontain makes great notebooks for fountain pens that won’t break the bank.
The reason for this has to do with paper composition and weight and how free flowing (liquid) ink interacts with the paper fibers. [1]
I think Pilot Kakunos (Medium nib) are the best starters. They're dirt cheap, and they write better than Lamy Safaris. Also, the grip is big and chunky making it easier to grip, while being made of resin and light. I started with it, and every other one I've tried has been worse than it.
For the best performance at a given price point, one of the major Japanese brands (Pentel/Pilot/Sailor). The Lamy Safari also performs very well, but is less durable, less comfortable to grip (for some), and may write somewhat wetter than you will be comfortable with as a new fountain pen user.
If you're a very occasional fountain pen user (like me), I have found the Platinum Desk fountain pen is very good at not drying out when left unused for longer periods.
It does put down a very fine line though, and it won't play nicely with crazy particle-heavy inks.
CHEAP: Lamy Safari. They come in plastic or in slightly more expensive aluminum (the Al version may have a different name, but it's the same size & shape and uses the same nib insert). These are gonna be $20-30 US, depending on your vendor. They are undoubtedly not as smooth to write with as my nicer pens, but they punch WAY above their weight, and deserve a spot in your rota -- especially clipped into a notebook you carry with you instead of something nicer.
ALSO INEXPENSIVE: Kaweco Sport. These are super compact when closed, so they fit into a pocket better than a conventional pen, and (like the Lamy) write better than their low-end price would suggest ($27 at Jet Pens; they also make them in brass for $90).
STEPPING UP A LITTLE: At $50-60, you can get one of the current "hot" affordable pens from TWSBI.com. They're pretty great; I have a 580 that I keep inked. You'll feel the difference between these and the lower-end pens. Be aware these are also a larger pen diameter-wise, and are thus sometimes less popular with small-handed people. TWSBI is also traditionally bottle-fill only -- no cartridges -- which puts some folks off. Don't be one of those; buy some bottled ink! You can get more variety that way. Plus, TWSBI pens in particular have enormous ink reservoirs -- I can write 2x or 3x as long with mine than I can with any of my other pens.
OK NOW YOU GET TO SERIOUS PENS: I had a good dot-com boom, and bought some spendy pens, but what replaced them ALL as my daily driver was the classic Namiki / Pilot Vanishing Point. They still make this pen, but a recently introduced variant of it has stolen my heart: the Decimo. It's the same style and mechanism, but just a little bit smaller in diameter. It makes it more comfortable to use, even for me with larger hands. Both kinds of Vanishing Point are ~$140-150, and well worth it. As a bonus, the carts for this pen are widely available in multiple colors, and the ink feels good to write with and behaves nicely on most sorts of paper (this can be an issue with some pen/ink combos).
That's the reason I used ONLY the Vanishing Point for the years I traveled all the time. Cartridge use seemed to work better on planes than bottles for me.
ANOTHER FINE OPTION: My sister gave me an Aurora Ipsilon a few years ago, and it's just a JOY to write with. I use the converter and bottled ink with it. It's been inked & ready to go since the Christmas Day I unwrapped it. About $120 at Amazon.
https://www.lamy.com/en/lamy-safari/