Well, it really depends on what you mean by 'best.'
I would personally say that the acekard is one of the best cheaper cards. It doesn't have a ton of features, but it performs exceptionally well for it's price.
If you want something with a ton of features (such as Real Time Save or and ingame text reader), then the Cyclo or the Supercard DS ONE would be more fitting.
P.S. Wrong section. Don't worry, the mods will probably move it :]