If we go by its ergonomics/identity as a handheld, it ranks low. I would say most backlit (or at least frontlit like GBA SP) Nintendo handheld platforms/models are better. GBA SP, DS/DSi models, and 3DS/2DS models all feel like pure handhelds despite their hinges causing some issues.
Switch is not pocketable unless you have comically large pockets or huge pants with large pockets overall that don't seem large compared to the pants.
The library is easily the best of any Nintendo handheld, and I'd even say home console as well.
A Switch Mini/Switch Pocket the size of a smartphone would be interesting. The tech exists, of course. It would basically be the size of a PS Vita 1000 but with far better specs crammed into it. I doubt we'll get one because Nintendo wants large profits and cramming Switch's architecture into a smartphone size is not that profitable.

Eh... it sort of depends.

The system I like best for a train ride is my 3DS still due to the kinds of games and form factor. But if I'm on a week long vacation, definitely would go with the Switch for the overall library.

Personally? Dead last. But not because it's objectively last. I just had more memories and fun with Gameboy through 3DS. Objectively, though, it's hard to argue with the Switch.

1. GBA/SP
2. NDS
... GC
4. 3DS
5. Switch

The reason why I ranked switch last is, because
A) games dont matter, I only look at the hardware
B) The only thing rivaling the switch in terms of hardware problems due to poor quality is the 3DS, but that one at least doesnt scratch its own screen.
C) Battery life is dog-shit.

GBA/SP are my no. 1 Nintendo HHs because they were awesome for the time and still are.
The way they lie in your hands, how the housing feels, great battery life, easy to fit into your pocket, ...

Tough question to answer. I want to say first but it has some drawbacks as a handheld in some situations. The GBA/DS worked much better as a system I actually would take out with me. Switch is a huge step up for handheld gaming but is something I generally wouldn't use outside the home.

Switch, because I can play it on the TV with a real controller.

#1

It's the greatest Nintendo system ever made. Handheld and console.

Damn right!

Switch is the best Nintendo console overall.

1) Nintendo Switch+OLED+Lite.
- Massive games library, some issues with hardware. (Joycons). But a non issue if you use it as a fixed console for it's entire life.
Some of the best selling and highest rated games of all time.

2) Nintendo 3DS+2DS.
Took the best aspects of the DS line, including full backwards compatibility with a larger display, better audio, better processing... And what will end up as the only console with glasses-free 3D displays... Backwards compatability is why it sits above the DS.

3) Gameboy+Gameboy Pocket+Gameboy Colour.
The handheld console that started it all with some of my favorite games like Zelda: Links Awakening.

4) Nintendo DS+DS Lite+DSi.
Never resonated much with the DS, but it's to ignore it's extreme levels of success and unique dual-screen+touch approach to gaming at the time.

5) Gameboy Advance+Gameboy Advance SP+Micro.
Mostly just a portable SNES, never really cared to much for the device. The lack of a backlight with the initial release turned me off.

6) Nintendo WiiU.
Some of the best selling and highest rated games on the Switch... Are actually WiiU ports.
It's portability was limited to a room or two, but it was a unique concept, just technically flawed.