What brand to you see as underestimated in the marketplace and with collectors?
For me, it's Wearever, I have several and they are great pens. I have three Zenith pens with gold nibs, all are great writers and less than $25. I have a Burgandy colored pen with Parker Brown ink and it writes smooth with just a hint of feedback on some paper. The pen is always ready to write, which is more than I can say for some of my better brand pens.
One of my newest pens is a Pennant. This pen has a unique nib advertised to always be ready to write. It's a medium, but closer to a fine medium. What's cool about the nib is that when you flip it over and reverse write, it does a good job and makes a nice extra fine line. More toothy, but not unusable by any stretch.
Everyone is gaga about Esterbrook, which was in the same market as Wearever, but their pens are more in demand. Few have gold nib and none of those can be bought for a $20. I'm sure there are some Wearevers that aren't vintage, just rubbish, but that goes for all brands.