Which is better: iPhone 4S or 5S?

My current iPhone contract is ending and I can actually get a $50 credit for a new iPhone if I sign another contract. I'm debating between the 4S and 5S. I like the 4S because it's smaller and I have lots of cables and adapters for it already including an FM transmitter for my older car radio. However, new is always better. Is the 5S really that much better than the 4S?

Added (1). OK. I guess I meant "iPhone 5" instead of "iPhone 5S".

The 5S didn't even come out yet.

The iPhone 5s hasn't been released nor has it even been announced.

The iPhone 5 is indeed faster than the 4S. It also has better screen resolution than the 4, and you can use all your existing accessories with it, but you'll have to buy a 30-pin to Lightning Adapter. Unless you already own a variety of cases for your current iPhone that you want to continue using, the size difference is negligible.

The iPhone 5 is just a better device, if the prices are anywhere near equal. You'll get at least one more iOS revision out of it to boot.