The 3ds has a slightly bigger screen than the ds, ds lite and dsi. So if you had no problem with the size of the ds screen, I would go with the 3ds. But if you found the ds screen a bit small, then by all means go with the 3ds XL. And with the money you save you could spend it on other things.
It's free to play after you buy it. That's F2P genius. ~ Brutal_Felix