I collect by theme or maker. Have always been a knife guy ... most often with one tactical and one traditional knife in tow. Retired from the USAF in 2000, got a business license and became a knife dealer. Sold enough Microtechs to become a "Microtech Certified Dealer" and still have the letter from their CFO advising me what I needed to do in order to step up to "Microtech Certified Distributor" status. At the last minute, the owner decided he had too many distributors and told me to urinate up a rope. Told him, "No, you urinate up a rope, I quit", then proceeded to sell MT ultratechs to anyone at dealer cost. Sold a lot of them which killed the price of their cash cow

Had a lot of nice custom Microtechs come through my hands, kept most of the rare ones, protos, Brends, and Tony mirror finished blades.
Sometimes I grabbed every plain edge SKU, like these MTX2s
Or one of every color.
After closing Chief's Cutlery, my interest began shifting to traditional knives. Almost became a GEC dealer but after buying one knife as a from them as a dealer, decided against it. Retired plus working full time for AT&T didn't want / need to use my time off to make more money.
3.5" plus or minus a little is the sweet spot for me, single blade first preference as blade rub bothers me. When my custom traditional made by a local friend had the backspring break, was on the search for a replacement. About this time TC barlows hit the scene and was lucky to score a couple from CC, single blade clip points. Wow, they were the perfect size and made better than any other factory offering. Only carry one traditional knife at a time, but have this inherent need for a backup, just in case. The search was on for more single blade TC clips, some runs were less than a dozen, the quest was on! Though diligence and some help from friends, have managed to get them all but a couple. Don't care how much they are worth, wish GEC would make enough to fill demand, re-release is fine by me. Evan rehandled a walnut TC which I carry everywhere.
GEC single clip 15s are the perfect traditional for me, sound, size, halfstop with flush backspring, and SS. Managed to grab one each of GEC's 2016 SS 15s single clips (and a couple doubles not shown)
My dad retired from the Rock Island Railroad as a conductor and I worked there before joining the USAF, so GEC conductors find a home here too.
In customs, I still stick to a theme, like ivory WTs.
Or by maker. Rick and Bret are both local to me which helps.
Won a couple in the Blade lotto, got a couple from Tony, a couple from dealers (thanks Vince for the stag trapper second from the right, my favorite traditional), and the remainder from the forum.
Rarely do I sell a knife, so am pretty picky about what I buy.