Vita of course! It play's Vita, PSM, PSP, PS1, PS3, and PS4* games! It has arguably the largest and most diverse library of any system ever. Plus with the chance of PS2 games coming to PS Now it could be like owning every Playstation console.
*Requires PS4 Add-on accessory
PSN: extremeM
PlayStation Vita Japanese Software Sales (Media Create Physical/ Famitsu Digital)