It changes every few years.

My first was the Pilot Metropolitan. Still a solid pen I recommend.

My next favorite was/is a PenBBS - perhaps the 309 - I don't have it on me at the moment. I replaced the nib with a Goulet nib, and somehow made it extremely smooth. I've not been able to make any other Goulet nib that smooth - somehow got lucky.

These days I'm heavily using a Platinum Plaisir which is also surprisingly smooth (no modifications).

Every time I've paid more than $50 for a pen, it hasn't been worth it. I can't get the ink in my Opus 88 pen to flow consistently. I'm sick of it.

I'm partial to Faber Castell nibs, but the pen I bought had a grip that I didn't like, and I don't want to spend the money to try their other pens.