Personally, I'd go for the R4 myself
I have an M3 DS Simply (Exactly the same as the R4), and it works fine, full compatibility for most games (Although with some games in the future you may have to wait for firmware updates.)
Why R4? I am not aware of any advantages it has over the CycloDS?
There are many. I own both cards, and while I use the CycloDS Evo as my primary card, I keep missing my R4.
Here's my list:
The IGR works almost all the time on the R4. The IGR doesn't always work on the Evo. (Example: Advance Wars: Days of Ruin!)
Even though the R4's file system isn't as pretty as the Evo's, I prefer it. The Evo's system has one major flaw: scroll sensitivity. It's very easy to scroll past your intended selection.
You can boot to the GBA slot easier on the R4. With the Evo, you have to hold a button or dig through a menu.
Though it's much maligned, I happen to like my spring-loaded microSD slot.
The R4 lets you create backup saves.
The R4 boots up faster, but it takes longer to load up games.
The R4 automatically skips the health warning screen. The Evo requires you to hit a button.
The R4 has no loading screen. The Evo has a fixed loading screen with that ugly boner-cross logo.
The R4 has a better shell; the edges are rolled. The Evo's edges are hard. The black Evo has that ugly white logo which is visible when the card is installed. Some black Evos also have problems with the microSD sticking out.
The Evo isn't a godsend. Really. It's okay. There are only a few things that I like on the Evo.
1. microSDHC support (though I've found 4GB to be overkill - I have a bunch of content I never play)
2. RTS ... when it works
3. Autoloading the last NDS file played (hold L+R through the boner-cross loading screen)
4. You can't accidentally delete things off the card