There's nothing wrong with Samsung's Touchwiz UI. In fact it provides some enhancements over stock Android, such as the ability to split the screen between two apps on some tablets. The only drawback is that it bakes some Samsung apps into the firmware, but you don't need to use them or even see them on screen if you don't want to. Looking at your screenshot, the only give-aways are the format of the download arrow on the WiFi signal indicator in the notification bar and the layout of the Nook, Home and App Drawer buttons at the bottom. Hardly noticeable and certainly not objectionable.
However KitKat is a two year old version of Android that was optimized to allow it to run on less powerful hardware. When a new device is listed as running Android 4.4, that's a clear sign that it does not have enough horsepower to run Android 5 (Lollipop), let alone Android 6 (Marshmallow). Depending on what you want a tablet for, that may or may not matter.
One of the great advantages of Android over iOS is the ability to customize the interface endlessly with widgets, instead of a grid of icons like iOS. I like to set up my home screens so that I can see at a glance all kinds of information like the time, local weather map and forecast, my calendar, todo list, etc.., without having to open any apps.
I'd suggest that you play with Android on the Nook you have before thinking about getting another tablet. In particular, explore what's available on Google Play (the Android app store) and try things out. As you become more familiar with Android and how to use it, you'll get a much better idea of what you might want in the next one.