OK that's a hard one... let's see...
Handhelds I have:
DS Lite
DSi
3DS
PSP
PSVita
REVIEW
CONSOLE DESIGN
When it comes to design, I'd choose ds over psp but psvita over 3ds (dsi was stupidly designed).
DS Lite
good points: smooth surface (fk yeah I sooo loved touching it), smooth buttons that didn't make obnoxious noises, analog volume thingy (dunno how to call it), stylus on the right side
bad points: screens are a bit small (compared to DSi) and back then we diddn't have the XL sizes... which are a no-no for ppl with small hands like me
DSi
good ponts: bigger screens, stylus on right side
bad points: volume buttons.... like NO, it was the worst choise ever, srface feels rough, buttons make noise
3DS
good points: even smoother surface /(^ω^)/ , analog volume thingy, cool circle pad
bad points: stylus in the back, small touch screen
PSP
good points: one screen only fk yeah (keeping up with two screens is hard )
bad points: bulky, analog pad is not the greatest, volume buttons
PSVita
good points: one BIGGER screen, slim and smooth, rear touch pad, two analog pads, smooth buttons, uses same charger as smartphones
bad points: volume buttons again... wtf sony?
FEATURES
DS Lite: nothing besides pictohat... boooring
DSi: camera, voice recording, FREAKIN FLIPNOTE BEST THING EVER, pictochat (and they added multicolored pens XP ), slot for SD card (not included), internet browser
3DS: camera, voice recording, face raiders, miis, e-shop, AR games, slot for SD card (included ), option to change themes, internet browser, 3D feature (upper screen only)
PSP: internet browser, cool themes (i have a hakuoki theme ) don't remember much tbh, haven't palyed in a while
PSVita: awseome menu welcome park, ps store, internet browser
GAMES
DS Lite/DSi: I had that one only for pokemon tbh, although I've played other games as well (pretty much pet games such as nintendogs, catz etc)
3DS: again, I got it for pokemon but eventually played other games (FE Awakening, Smash Bros 4, Hakuoki etc) as well and still have more I want to play
PSP: tbh the only game I've completed on PSP is YS Seven (awesome game ) I actually started using it only recently, I had it left alone in some drawer, forgotten... oh, all the cool games I've probs missed... I have downloaded a bunch to play but I don't really have time rn ._.
PSVita: at first I got it because why not... there are tons of games I have on my wishlist now... how great the only one I've completed is Tearaway and I'm also close to completing Ys Memories of Celceta (loooooooove :3 ) aaand I need to resume Gravity Rush sometime (nice game but controlling gets on mah nerves)
Obviously, picking one is hard but I'll have to go with PSVita because I enjoy playing games on it the most and I have loooots I wanna play (I just don't have the money TT^TT )
long post is long
I regret nothing