Perfect knife.... pure opinion and will vary with the person and use.
I don't collect knives, but I do accumulate them and the many I never use are a testament to this. Right now I prefer a knife that has a blade about the size of the Spyderco Delica in a modern and generally 4-4.25 closed length on traditionals. I prefer two blades on a traditional. Over on the traditional forum, barlows tend to be popular and especially the ones Waynorth orders from GEC. I love a barlow, but they are too small for me for now. I may change as I get older or the wind blows from another direction.
So, perfect varies with time. In terms of buying new knives, I prefer to be somewhat spontaneous rather than carefully researching a knife and then buying. I do have certain brand preferences because of predictable quality. If it looks good to me, it is probably okay. If I don't care for it, it goes into my tub of unused knives.