Most of mine are collected by theme.
Until recently mainly gentleman-like knives, but recently I have become more and more interested in classic regional styles.
I usually do not like aggressive knife styles - I often think they look vulgar, esp those with tanto blades.
And many modern folder knives bore me a bit. As an example, I have a Delica ZDP. A very good folder, excellent in fact. It's nice to use, but I notice I barely carry it, while I keep on selecting a Laguiole, an Eka Masur 88, a Kiwi, an Opinel, more recently also the Buck 110, and the like -more than any other knife in my collection (well the 2 exceptions are the Boker Trance and the Fallkniven U2 which are probably my most used "modern" style knives - but far behind the other ones). In some way, I find that these knives have much more charm.
I played a few times with a Griptilian in the shop. Of course it's splendid, probably of similar quality as the Delica, but I didn't buy it as I would probably rarely use/carry it. I am now looking forward to the delivery of a few classic knife style examples (Nontron, Douk-douk, a
special Opinel); and the incredibly beautiful
Le Thiers gentlemen knife from Fontenille Pataud. Check it out, it is in my opinion one of the classiest knives on the market.
To continue the trend, later on I expect to order a
gentlemen knife from Moki, a heavier "sports"-variant of the classic Laguiole (perhaps a
Fontenille Pataud, but actually the more affordable yet similar
Puma might be good enough), an
Okapi, and a compact
Canadian style Bark River.