Welcome to the wonderful world of fountain pens. In my personal experience, I have found that Cross has some wonderful pens. They have very nice smooth nibs and the medium nib is a little finer than the normal medium. In addition, look for A. G. Spaulding. Those are Japanese pens with excellent smooth nibs. The ones I have have the wooden barrels that are very nice in the hand and they use standard ink cartridges. Just one note, I have found that the quality of writing of every pen I have in my collection (I can't believe I just said that, I guess I am a collector after all) depends a great deal upon what paper I match the pen with. I have one Mont Blanc (a gift from my thoughtful better half) and the flow is so nice that when I try to write on paper that has too open a weave it give far too broad a line. On the other end of the spectrum, if the paper is too smooth, too tight and especially with too much sizing on it, it doesn't write well either. Especially if the paper has too much sizing. I had one very expensive notebook a couple of years ago that I found I simply could not write in because every pen I tried clogged, even ball points. Very depressing.
Anyway, to sum, the key element to a fountain pen is the nib, whatever the cost. You don't have to spend a fortune to get an instrument that will serve long and well and become a favorite friend.