If upgrades/updates for the operating system are a priority for you than it would be better to migrate to an iPhone. But if you want to stay clear of Apple's oversight and stay with Android, while Motorola does have some really good phones it isn't going to be best option for consistent, regular OS upgrades Also, the general trend is for longer term support for higher end models, and less support for lower end models. There's some overlap in that but for the most part Android support issues are just too unpredictable. Here's a good read on the matter, a lot of it based on recent history summations (something that can be accountable, but can't be a 100% thing as the market just has too many variables):
https://www.computerworld.com/article/3336930/android-upgrade-report-card-pie.html