The prices of Killstreaks (especially Professional) are incredibly skewed, as one person might like one effect/sheen and one may like a different one. It all goes back to personal preference, and it's not uncommon for a more expensive version of an item, like in your example, of a Collector vs Strange, to be different. Just use your own judgement when buying, since just because you like it and buy it doesn't mean you will be able to resell it as easily.