Does the iphone 6 come with a SIM card? Also does the 5s come with one too?

I'm on a contracted plan if that matters.

It depends on your carrier. If you have AT&T It will have a SIM card more than definitely, but Verizon more than definitely won't.

Yes, if you order the phone online it will come with one

Depends on the package you buy, they sell iPhones either on their own or with a sim. If you're buying straight from Apple then they will ask if you want a sim with it and what carrier do you want. Check on Apple's website for details on the sim plans they currently have.

It depends on how you buy the phone in terms of configuration. If through a carrier, yes. If unlocked, no. This concerns both & all iPhones or even phones in general.