If you are looking for regular updates/patches on Android smartphones, then always go for Nexus-branded/ carrier compatible high-end unlocked smartphones i.e. Nexus 5x/6p/Samsung S7/S7 edge/HTC M10/LG G5 etc.
Carrier locked midrange smartphones hardly ever get updates/patches. Moreover, high-end carrier locked smartphones get delayed updates/patches and their update cycle is quite small.