In this Just a Thought I discuss the state of the iPhone and some good upgrading options for you depending on the phone you have, from the 5 all the way to the X. Summary: Buy the 6S if you have anything older than the 6S and wait for the new 2018 phones if you have anything newer. If buying used, buy in "Great" or "Mint" condition, with some sort of warranty. Don't buy phones with replaced screens.