The PSP is on the way down, IMO – game sales are flat, there aren’t any (as far as I know) compelling titles on the horizon, and even the UMD movies aren’t selling. People are apparently buying PSPs and using them as media players, but I don’t know anyone who actually owns one.
The Nintendo DS Lite, on the other hand, kicks so much portable gaming ass it’s not even funny. The screen is hands-down the best I’ve ever seen on a portable, and the DS game library is starting to really pick up steam – between tried-and-true mainstays like New Super Mario Bros., Mario Kart DS, Tetris DS, and StarFox Academy, and “adult-oriented” games like Big Brain Academy, Phoenix Wright, (lawyer-based RPG) and Trauma Center (surgery simulation) makes it more original, IMO. The built-in Wi-Fi makes it damn easy to start impromptu multiplayer games, and now that more games are coming out with internet play means it’s even more viable.
I’ve only acquired a NDS about a month ago, but I seriously think this machine is set to take the world by storm in the near future.