Out of the two? SuperCard by far. But out of all of the flashcarts, I'd say either the SuperCard DSTwo, CycloDS, or the Acekard 2i.
If you really wanted to look at an R4, I would suggest the original due to the new firmware making the R4 as good as the leading cards in terms of game compatibility. If not that, CycloDS or Acekard2i. You can look at the Supercard DSTWO, but there is no way of knowing yet if it will be worth the money.
I'm gonna have to go with the M3 DS Real/M3i Zero on this one.....it has a ton of features and has a real team backing it up with new firmware updates at least once a month. It's also capable of running at least 3 firmwares, so you can pick which one you like best or switch between them on the fly. It's got RTS(Real Time Save) Functionality and RTG(Real Time Guide), plus the sakura firmware is awesome and so sleek.