I'm currently having a difficulty trying to decide which phone I should get. I have S8+ and iphone 8 for usage at the moment and I must say I do enjoy Samsung more. Does Iphone X has something extra ordinary than the Iphone 8?
Personally, I am not a notch person, so the S9 Plus would be my pick. I actually have an S9 Plus and really enjoy it. I originally had the purple but my mother decided to pinch it on me a few weeks ago so I went and got the grey. The S9 Plus has been my first Samsung device since the days of the Samsung Galaxy Nexus and I am extremely happy with it.
There's not a lot of difference between the iPhone 8 and the X. The missing home button being one main difference. The 8 and X came out at the same time so you wouldn't be trading up to a newer device. Just a bit of a different one. I like the iPhone X though the lack of a physical home button took some getting used to. The physical home button does make it easier/faster to unlock the phone without having to aim it at your face all the time but you get used to that.
One other thing to consider is software updates. Apple supports older devices for longer and updates their software much faster. iOS 11 works on any iPhone starting with the 5S up to current devices. The 5S was released in 2013. Samsung tends to take a very long time to release updates and ends up abandoning devices after about 2 years on average. Compare how long updates take to reach Samsung devices compared to when Google releases them.
My daughter has the S9+ (purple!!!!!) and loves it, no issues at all, though some people had dead touch zones soon after release. I'm unaware if that issue still exists. But you can test a phone screen for dead zones in-store before purchase.
As for bad apps in Playstore, something like Norton scans all apps. There are so many ways to screen apps that no one should ever fall victim. I don't know anyone who ever has.