AFAIK, your credit score grows more as you spend more in relation to the total credit available to you, up to around 50% of it.
So lets say you have four cards with a $25,000 limit on each. That would mean you have $100,000 credit available. And the most gain you can get comes from spending $50k a month on any combination of your cards, and then paying it down to zero right away (and occasionally buying gum or whatever on the unused cards so they stay active).
If you cancel two of those cards that you never use, your available credit will drop from $100k to $50k, but now you only need to spend half as much to get those max gains, or since you probably don't nearly spend that much, what you do spend takes you twice as far towards building your reputation.
Cancel all of your cards that come with annual fees. They're not worth hanging onto. Keep your first card, because it sets a "start date" on your credit, and you want that to stay as long as possible (unless your first card had fees, then maybe just think about it). Keep your best card (which I guess is your new Amazon). The rest you can toss. Unless you really need a big credit limit.
