Post Paid plans are usually with a contract and for X years. Most expensive, widest coverage for that given network and usually best customer service tho you may have to try many times to find the person to fix your issue.
Prepaid plans from like Verizon or ATT usually not as large coverage area (no roaming) but still very good coverage, no yearly contracts, less expensive.. CS less than Post Paid, often online.
Prepaid from resellers like TracFone, StraightTalk, Red Pocket, H2O (called MVNOs)... coverage usually the same as the prepaid of the network you are on but even less hand holding. Cheaper than Prepaids from Verizon ATT, etc. May buy your monthly plans via cards from Walmart, Target, Dollar Store or online places like Callingmart. Cards often at discount to list price.
After many years of smartphones, the next one I buy is going to be unlocked and usable on any network so it is easier to switch networks, plans etc when I need. I have a Google voice number so it is not an issue should I lose my phone phone number when switching companies.
Also playing around with one of the flashed jetpac things with unlimited data for a low, low monthly price but you need to be comfortable with phones, plans coverage before jumping in that boat. IMO
