Samsung lost me as a customer this year with the mess of the S6. I know, one person, wow, but I think Samsung has lost the support of a lot of more advanced users in favour of your average "I just want a good phone" type of person.
Touchwiz on the S6 was a mess, 3GB ram but can't multitask better than a Moto G, average battery life at best, disappointing update (that took ages to release) from 5.0.2 to 5.1.1 that didn't fix the multitasking and a horrible antenna that picks up signal worse than their own Galaxy S4 from 2 years previous. Add the awful customer service I received when trying to fix these issues, and you have a huge mess seen as this is a flagship that launched at about £600.
It looks really nice, it's super light and thin, but none of that matters if the experience sucks. If Samsung want to put out products like that and charge a fortune, they are going to need to do a better job.
Otherwise, Apple is more reliable and easy to use for your average smartphone buyer and other brands like Motorola/LG/HTC/OnePlus will appeal to the more technically minded/advanced user.
At least Samsung used to try to appeal to advanced users, but not anymore now that they removed microsd and removable battery support. And now that they are using their own in-house Exynos chips, you can't even run stock android, you have no choice but to use Touchwiz.