What other knives do you have? I recently (last 2.5 Months) bought an Umnumzaan and a Large 21 (Inlay) so I was at a similar crossroads. I went for the Zaan first because I liked the uniformity of the milling, price, size and blade shape. I ended up adding a 21 because I wanted to experience it. I went for a drop point for that one with wood inlays, which match the Zaan pretty well in terms of color (the former is bronze anodized, the latter has striped platan inlays) and with the 21 having slightly thinner stock they compliment each other quite well (in my opinion at least).
I don't see the point of the 31 personally, it feels like it's turning the 21 into an Inkosi, so it's a non existent gap in the line up and the new inlays look...meh? It looks better in three pieces, again just my opinion. The plain jane one's look a bit boring to me, just because I am not a huge fan of plain Ti scales.
I got big hands and I would give the Zaan a very minor advantage in terms of feel in hand, but aside from that they are very comparable. You can't really go wrong with either. If you have more specific questions, I am happy to try and answer.