I don't have a lot of pens to use as a basis for comparison but I really enjoy writing with my Vac semi-flex nib because I can use it daily and it still gives some line variation that makes the writing look nicer. (Yes, I ended up w/ a vac rather than the Pelikan because I couldn't resist the vac's prettiness).
My Mabie Todd flex nib flexes easily. It's not a wet noodle (my basis being other people's pens that I've tried) but it's great fun to play with, especially now that I've broken it itn.
For stiff nibs, I prefer the Esterbrook 9556 and the Parker 75.
All of these pens have a wee bit of scratchiness to them that makes for an interesting writing experience. I had started preferring smooth nibs with no scratch, but it turns out I rather like the slight resistance and sound on the page.
One of those rather difficult questions!! Seems to be a changing "fad" , so I think I'll simply say what I use most..in no particular order
Conklin Symetrik with firm medium ( slightly smaller nib than on the more common Endura Symetrik models) , Sheaffer Snorkel with a flex stub , Sheaffer Imperial SS TD with a firm fine, PFM V with a firm fine and a Swan 3240 with a medium semi-flex.