Which do you prefer? I personally like the DS Lite better and am in AW that they have better screens than some n3ds.
Why would you even consider buying a DSi with the 3DS out there?
I'd choose NDS over DSi anyway because of backward compatibility with GBA titles.
The encrypted support for Wi-Fi connections is literalli useless since DS online services are suspended.
The DSi (and 3DS) had The Legend of Zelda Four Swords Anniversary Edition which is a fun local multiplayer game.