Finding good pens for particular journals is always bit of a journey, so when I do find one, I generally tend to stick to them. And for moleskine sketchbook, my choice of pen so far has been Pentel Energel 0.7. But in the middle of this journal, the last Pentel Energel I had ran out of ink. And so I searched through my pen pot for a suitable substitute, and found Pilot Frixion - which turned out to be fantastic. Pentel Energel is still my first choice - because Pilot Frixion is not as dark. It's meant to be erasable, so the softness of its ink is understandable. The flow is smooth, and the ink sits well on moleskine sketchbook's thick pages. Just for practical purposes, Frixion is very comfortable, easy to use pen, which is important for me, since my journaling style is predominantly writing. Lots and lots of writing.
What about you? What are your preferred pens for moleskine sketchbook?