The DS is the one to get for the best future support ATM. Neither the PSP nor the GBA have a projected lineup as appealing as the DS' (this is subjective, of course, but I think you'd have a much easier time proving it than the opposite scenario).
As for the PSP, consider how highly you place non-videogame media in your portable priorities; if you would like to watch movies and listen to music just as much as you'd like to play games, it might be the better buy for you (although it's well over your quoted budget).
The GBA I'd skip out on, unless you're really concerned about price and portability; it has an inferior screen to the DS and has less software support as well (although Jarrod and company do have a point about the GBC and even original GB library, which you won't get natively on the DS).
Overall, for your budget and for the quality of the upcoming software (as well as a few decent games out now), I'd say go with DS. It's admittedly a shitty machine, but its future lineup makes it worth owning.
As for the PSP, consider how highly you place non-videogame media in your portable priorities; if you would like to watch movies and listen to music just as much as you'd like to play games, it might be the better buy for you (although it's well over your quoted budget).
The GBA I'd skip out on, unless you're really concerned about price and portability; it has an inferior screen to the DS and has less software support as well (although Jarrod and company do have a point about the GBC and even original GB library, which you won't get natively on the DS).
Overall, for your budget and for the quality of the upcoming software (as well as a few decent games out now), I'd say go with DS. It's admittedly a shitty machine, but its future lineup makes it worth owning.