PSP

Well, if they can't give you a good reason, you probably shouldn't listen to them.

My opinion? I buy systems based on the games. I didn't buy a PS2 until I was sure GT4 was around the corner. I bought a Gamecube because I wanted to play Wind Waker and Animal Crossing. I don't have an XBox because there aren't really any Xbox exculsives that I'm interested in. So, if you like the games coming out on the PSP, go for it.
 
The PsP in its current state is just not worth it for me. Not a big fan of the launch titles, being able to watch movies and listen to Mp3's is very nice but not worth the $250+. I rarely would be in a place where I would need a portable movie player.
 
Right now, though, PSP has a better game lineup than the DS. Sure, the DS has the likes of Mario 64, Warioware and Zoo Keeper, but that's about it. While PSP has Dynasty Warriors, Metal Gear ACID, Mercury, Ridge Racer among others. But the DS does have some nice games looming on the horizon, like Jump Superstars, Dynasty Warriors DS (cough), and the various FFs.