AT&T, is it cheaper to get 2 year contract or AT&T Next (you pay every month)?

Well, I'm really confused here.

My parents and I had the family plan for our phones and they were all 2 year contract. We pay over $100 every month for all the costs like network, phone bills and everything. I have 200MB of data plan allowed any extra will cost me $15. BTW, every message we send or receive costs money.

Well, that's basically everything I know, I have no idea how the 2 year contract really works, why do I have to pay so much every month(it's a lot to me, or is it normal to pay that much?) or why does every text message costs money.

Now it's been over two years and the contract seems to continue(?), but I wanna get an iPhone 5s, so what should I do? When I go to the store what should I tell them? What about the 2 year contract for my family's old phones? How does the family plan works is it better if I don't get it? I'm thinking of getting the AT&T Next instead of the 2 year contract because I don't want to use a phone for 2 year anymore. And my parents are not getting iPhones but me.

Sorry, I know this is long, I may not express well, and I sound like an idiot, but please try to answer as many question as you can or at least the question of the title. Do you have to pay for the messages and other stuff for over $100 as a family plan if you get AT&T Next?

Apple says I have a glitch on my iPhone and for a $140.00 support tech fee they will fix this. I just had my phone factory reset by Apple. They know there's a problem, has been since day one. What can I do other than pay this fee to fix my phone?