I think asking this question in the 3DS forum instead of General Consoles is gonna lead to your answer.
The 3DS looks to be a good alternative to the DS, honestly. It's got better features than the DSi and the analog slider is a good plus for any games that move in a 3D environment. I'd take it over a larger screen, honestly (and at the same price). As a standalone system, I wouldn't even start with it until sometime next year. Mario Kart 7 looks fulfilling by my standards and it has a few "candy bar" games (short but sweet) coming up but I'm still finding it lacking when it comes to a big meaty game, outside of the endless replayability of Tetris Axis. Wait for a Pokemon game to come out for that area to be filled.
I'm a Vita guy myself and crossplaying with a few games really helps quell my fears of the dreaded "dead zone" that was PSP online gaming. At least now you can play with PS3 owners of games (I think Wipeout and UMvC3 both support this, for instance). It's a bit pricier but if you were willing to shell out $250 for a 3DS then there's no issue. The new media kinda sucks but you buy one cart and you'll probably be set for your lifetime. I'm liking how it's coming out mostly, minus a few things but overall it's gonna be my handheld for the next gen. Maybe I'll get the 3DS cheap one day used and use it to replace my piece-of-shit DS Phat.