Well, this obviously depends on your preference. These days, choosing a cellphone often depends on what kind of computer you use. If you are a Mac user, iPhone would be a good bet because it syncs seamlessly, whereas for a Windows user, an Android might be more convenient. Here I have compiled a list of the best phones currently available for less than $500:
iPhone 6 and iPhone 6 plus - store.apple.com/us/buy-iphone/iphone6
Moto X - www.motorola.com/us/motomaker?pid=FLEXR2
Nexus 5 - www.google.com/nexus/5/