Sonic Ds games help me please!

[Gunstar Green]

They're all decent and cheap.

If I had to recommend just one though, I'd probably go with Sonic Rush. Amazing music by Hideki Naganuma though the level design has a lot of unfair pits. I still had the most fun with this one though. The dynamic between Sonic and Blaze reminds me a lot of Sonic 3 and Knuckles on the Genesis which is my favorite Sonic game. I think the parallel is pretty intentional by the designers.

Sonic Rush Adventure is pretty bland and has lots of pointless story bits and other unnecessary features that just clutter it up. It's still a fun game though with arguably tighter level design.

Sonic Colors is really good, my second recommendation after Rush. In all actuality it's probably the most solid one of the bunch.