This makes me want to see Google finally take Pixel/Nexus seriously and push its own SOC & terminals.
I'm currently using an OPO, but will probably go back with Nexus for my next phone...
Samsung however is very bad at this and they have replaced pretty much every core Android feature with their own most of which cannot be uninstalled easily or at all.
So if you really want a clean OS e.g. without Samsung Mail, Browser (which is the most insecure version of Chrome I've seen in a long long time) Keyboard and the other 10,000 Samsung services you have to flash it with an AOSP based ROM.
LG, Motorola, HTC and others usually offer GE devices when you buy it directly from them or trough the Google store.
As Chen notes, flashing is a very difficult process for "non-techies" and actually near impossible for carrier variants of flagship phones due to bootloader restrictions.