im in the same situation as you lol, except the last time i had a handheld, it was a gameboy color.
problem is, the only "good game" on release day of the 3ds is super street fighter 4: 3D
zelda, kid icarus, resident evil, star fox etc are going to be coming out like 3+ months after the 3ds releases... however, the 3ds has backwards compatablity and can play ds games so no use of getting a dsi imo.
up to you if you add $100 bucks more and go with a 3ds.