Another deep hobby for me. I've stopped buying, because there are only so many pens one can rotate through. I started collecting pens at about age 11... Got back into FPs in a big way about 20 years ago. IT all started because my dad gave me a ~1928 Parker Duofold as a teenager, told me the history of it - still have it, of course. My go-to pens are Parker 51s and 45s, but I have and use Esterbrook, Lamy, Sheaffer, Waterman, Indian eyedroppers etc. Sold my Montblanc 146 from college days many years ago, stopped liking the brand image a while back.
All in all, fountain pens are great values in the pen world, as you can refill cartridges and bottled ink is still (relatively) inexpensive. The cost of quality ballpoint and roller refills keep going up and up. I plan to sell some of mine off as finding the proprietary refills at a decent price is tough. A lot of rollers can be modified to use the Pilot G2 refills, which are great - I use those in most of my Lamy rollers.
Favorite? The iconic Parker 51. I used my first one about age 45 and regret the lost time before. Everyone should have one, IMO. All my aerometrics still have the original pli-glas sacs from the 50s. Like the receivers and amps we love here, the overbuilt Parker 51 gives pretty trouble-free service long beyond its expected life span.