I'd actually disagree with you, for me the PSP is just a smaller PS3, it uses the XMB format (At least I think it's called that) and for all intents and purposes plays the same sort of games.

For me the DS family is better because it utilises touch screen technology and is markedly different from it's parent console, the Wii and Wii U. While the Wii uses motion control, the daughter handheld instead uses something different. With the PSP, aside from a few minor changes, the controls are similar and is basically just a shrunken PS3.