I recently bought myself a lined Paperblanks journal in the "Old Leather" style, which is one of the plainer options available, for use as a commonplace book. Paperblanks journals are available in a multitude of sizes and cover designs, and both lined and unlined. I particularly liked one design that had a Dickens theme; the cover was based on a page of his notes for his novel Our Mutual Friend. However, I eventually settled on this one.
It is in the "Ultra Format", has 144 pages, Smythe-sewn binding, a standard pouch on the inside back cover, and "acid-free, sustainable forest paper" although the weight of the paper is not given. The covers are hard, not flexible, and feel very sturdy. One problem is that the finish of the cover is of the type that shows scratches very easily. Luckily, it probably won't be noticed on my version, which is meant to look like old, worn leather. I particularly like the design on the spine. I was concerned about the label, but it easily peeled off the cover without leaving any residue behind.
The wrap-around cover has a magnetic closure, which is completely concealed within the cover, so that there are no external magnets. It has some advantages over an elastic closure, which always has the potential to break or become stretched out of shape and is more fiddly to use. However, the magnet could be a problem if you are storing the notebook next to USB drives or other media. Perhaps this one is best left on the shelf rather than carried around with your other supplies.
The endpapers are gold, which harmonize well with the cover. The pages are a pleasant off-white. The lines are 8mm apart (a bit wider than I would prefer, since I have small writing) and are very unobtrusive. They do not run to the edge of the page, which some people do not like, but I do not mind because I like having that extra white space around my writing. I haven't written in many different notebooks or on many different papers, so I can't really say much about the quality of the paper itself. I do know that I certainly like it.
I did test a few pens on the paper:
(I apologize for this image being slightly out-of-focus.) Most of my pens are gel pens, so if you would like to see how this paper behaves with fountain pens and inks, I urge you to check out the review at Spiritual Evolution of the Bean. I meant to show you the back of this page, but then I mistakenly wrote on it (with another Zebra Sarasa). This pen showed through very slightly, but it is scarcely noticeable. There was no bleedthrough.