>>29888452The Switch is the Wii/WiiU successor
The 4DS is one more year away and it will look like the Switch but much more smaller, the controllers aren't removable and will have touchscreen support
Whether it will come with one screen or two screens like the DS/3DS is irrelevant
You also can't dock it and will have inferior hardware compared to the Switch but miles better than the N3DS
The XL version will be bigger than the Switch and have similar hardware but you can't play Switch games on it because Nintendo