What is the lowest selling console/handheld gaming system you have, and do you think it was worth getting or do you regret it, and why?

Lowest selling system

Neo Geo Pocket Color It barely sold anything. I got it dirt cheap with a few games and played it quite it a bit in high school...probably when I shouldn't have while in some boring classes. I'd say it was worth it. 

Lowest selling console

Dreamcast. I bought it after it was discounted for I think around $50 with a handful of games. More than worth the money. Sadly I've lost every game for it except Sonic Adventure.

PSP. I didn't really play much on it, so no, it wasn't really worth it. Its battery got bad too, so I think got rid of the whole thing (or maybe just the battery, if that's even possible) - regardless, I don't currently even have a usable PSP anymore.

I think the only thing I really played was Metal Gear Solid: Peace Walker, and I didn't really get very far in it either. It was good, but I guess the controls felt like they could've been better with a proper controller. I have the impression that I also started Metal Gear Solid: Portable Ops but played even less of it, possibly because of either terrible camera, poor controls, or both. It's quite sad that Portable Ops isn't available anywhere else, but at least Peace Walker got ported to other platforms.

It felt like a fun system, but I just didn't get into the games. Later I've also come to realize that playing on portable devices doesn't even feel like a great experience to me, which is a pity, but it is what it is.

The lowest selling system I ever owned was the TurboExpress portable (sold about 1.5m units).  It was pretty expensive for back then but it was absolutely worth it since it played the TurboGrafx console's games, making it the most advance handheld at the time by far.  Easily had the best looking screen too, but unfortunately, it was prone to having some burnt-out pixels - the first one I picked up had several but I exchanged it at the store for another with a better screen.  Stupidly, I sold it shortly after I (also stupidly) sold the Turbo console.

The lowest selling system I still own though is the Dreamcast.  The fighting game library alone paired with the arcade joystick made it worth it to me back then.

Vita.
Was worth it cause Sony started to give lot's of game for free or at a very heavy discount.

Gravity Rush, Soul Sacrifice, freedom wars, persona 4 golden and more... I got a lot of games for free or dirty cheap.

Saturn,Dreamcast and Turbografx-16. All are brilliant consoles. Some of my faves. DC is my fave console ever and Saturn is my 3rd fave ever. TG16/PCE has a ton of amazing shmups and the best version of my fave game ever. Ys 1.

If we talk past tense, I owned both a Vita and WiiU. I don't regret buying either.

Vita introduced me to Persona, Persona 4 Golden was incredible. I also enjoyed Wipeout 2048, Gravity Rush, Uncharted GA, Ratchet/Sly Trilogy, Rayman Legends, TT Walking Dead, LBP. I got a decent amount of use out of it and as I had PS+ for PS3 already I got a lot of free games for it.

WiiU I really didn't use for much, I basically bought it just for Mario Kart. I played a little bit of Mario Party 10 and Wii Party U but that's it. It was just an MK8 machine for me.

Both were very cheap when I got them though, about the £140 mark. Imported both from an EU Amazon site for cheap.

WiiU I got a little after MK8 released and Vita I bought December 2012.

Not sure if I still have my PSP Go but I have my Vita somewhere in my house.