When not using one of your fountain pens, what do you prefer? A ballpoint or a rollerball? Why?
I used to prefer a rollerball, sometimes even more than a fountain pen. But that all changed one day about 7 months ago. I was taking notes in a new notebook, and the amount of show through on the other side was unreal - especially for a gel pen. That's how cheap the paper was (I think it was one of those Made in Egypt Staples notebooks). So I had to switch over to a ballpoint, and then I got to experiment with all the different ballpoint refills and came to find that I love Parker ballpoints more than Cross (an old favorite of mine). After writing a bit with the ballpoint, it grew on me, and I ended up buying vintage ballpoints and modern luxury ones to see which ones I like best. Most recent acquisitions were: Parker 75 ballpoint in gold (love that pen!), Parker Insignia in gold (the Insignia line is perhaps my favorite), and a Pelikan K400 (like the Jotter, just a lot fatter).
I prefer pens that take Parker refills. Of the refills I personally enjoy are Parker's own QuinkFlow catridges (fine and medium points), Schmidt EasyFlow, Schneider Slider Broad, Staples refills for Parker ballpoints, Parker gel refills, and the various cheap refills you can buy in bulk on eBay that are either ballpoints or gel pens (found a gel pen a while back that wrote with a decently fine line). And I could've sworn several years ago I had a Parker-style refill that wrote with liquid ink, but I don't remember now.
Outside of Parker ballpoints - then I'd go with Waterman or Cross. Oh, and Montblanc! Montblanc pens write average, but they are so classy.