These are the top 5 most popular Nintendo DS/DSi Flash card, including iEDGE support DSi V1.4,DSL,R4I-SDHC,DSTTi ,R4i Gold and iSmart MM.I have listed all the features of those DS/DSi flash card and you can compare them to each other.
More details about DS/DSi flash card, please go to this site

No.1 iEDGE support DSi V1.4,DSL from EDGE team
# Features:
#Latest DSi firmware supported: v1.4.1
# Supports DSi/DSL/DS
# iEDGE comes blank without any copyrighted software, making it 100% LEGAL
# Fully upgrade-able bootstrap to combat future DSi firmware updates
# Supports DSi firmware v1.4
# Plays commercial NDS ROM
# Plays homebrew NDS ROMS
# Frequently updated OS for best compatibility
# In game reset
# Automatic ROM protection patcher
# SlowMotion mode
# Save game saves directly to Micro SD
# Automatic save game type detection
# Supports clean ROMs
# Supports MicroSDHC cards up to 32GB
# Multimedia playback such as movies and MP3's
# Action Replay compatible cheat system
# Multi language user interface
# Micro SDHC card reader included
# Full download play support

No.2 RED R4I-SDHC Upgrade Revolution for DS(NDSi/NDSL/NDS)
Features
● World New Download Engine For Games.
● A card provides all NDS games and unprecedented experience to the player.
● Users just one click away from playable games download.
● WIFI search engine function available with NDS/NDSi/NDSi LL. Users are able to search and
download the games and the latest game information according to their own preferences
anytime, anywhere.
● You will be able to manage your NDS/NDSi/NDSi LL download by distance control through WIFI
once you install our Games-Engine Assistant on your computer. Users only need to click on the
games they want to download on NDS/NDSi/NDSi LL and the games can be downloaded
automatically tothe assigned computers. This can avoid the annoyance of waiting during the
download process.
● Through our PC-based Games-Engine Assistant software, it is able to download our website's
NDS games quickly and easily.
● Core upgrade automatically through WIFI of NDS/NDSi/NDSi LL to avoid tedious upgrading steps.
● Able to memorize and restore to the previously selected game or application after restarting
machine and soft reset.
● Sleep mode function, for power saving and longer standby time.
● Multi-languages are optional, they are Simplified Chinese, complicated Chinese, English, Japanese,
French, German, Italian, Spainish and Dutch.
● Friendly interface, easy to operate.
● Realtime smart help windows.
● Integrated the latest Moonshell 2.0 Beta version.
● Game compatibility: 100%.
● No need to flash. Built-in launch Slot-2 (gba) function.
● Support SDHC micro sd cards (4GB、8GB、16GB、32GB).
● Support DMA read and no lag while using any microSD card.
● Support FAT16 and FAT32. Files can be transferred with PC, PDA, Cellphone and Camera.
● Support clean rom and drag-drop to play. Fast loading.
● Support NDS and iDS games. DS games can run on any DS versions.
● Files are to be saved directly to TF card, copy or restoration is not required.
● Automatically recognise saved new game types, no need to update the database.
● Support moonshell and home brew.
● Power saving design. Enter optimized mode automatically.
● Double screen UI, abbreviated picture and game title display, button and touch operations.
● Easy to use, setting or adjustment is not required.
● Support Wi-Fi, rumble pack and browser expansion.
● UI background can be changed.
● 4-level brightness adjustment.
● Support soft reset.
● Support AR cheat code.
● Support soft-reset of moonshell 2.0 (back to main menu of R4 NDSI by pressing START button).
● DLDI auto-patching.
● Support Download play.

No.3 DSTTi for DSi/ DS, Support SDHC
Features:

* DS original cartridge size, Slot1 interface.
* Plug 'n Play, easy to use, just Drag 'n Drop file from PC to flash memory card.
* No FlashMe, built-in NoPass, and the GBA cards in slot2 can be started directly.
* Supports CleanROM, No covert.
* 100% SDHC TF and standard TF compatibility up to 4TB(4096GB) flash memory card.
* High speed SDHC. Supports any TF card speed with no lag in game,
* Save directly to TF card, not to onboard chip, Never lose your saves.
* Automatically detect and generate save type.
* Supports Moonshell and homebrew. DLDI auto-patching.
* Supports FAT/FAT32, works on any OS.
* Supports Action Replay cheat and edit the code base.
* Built-in energy-saving design.
* User friendly skinnable interface. Touchscreen or button operation. Supports Skin DIY.
* Supports the "Hot-Key" SOFT RESET.
* Supports the WiFi game, DS Rumble Pak, DS Browser.

No.4 R4i Gold Revolution for DS(NDSi/NDSL/NDS)
Features

-First card to hack DSi 1.4 version firmware
-Compatible with multi-language for all DS editions
-Support Action Replay cheat
-DLDI auto-patching
-Support all SDHC cards(Micro SD 4G,8G,16G,32G)
-2nd generation storage device (no booting tool required)
-Flash fitting slot 1 card
-Uses MicroSD card, FAT16 or 32
-Supports any MicroSD card speed with no lag in game
-Supports Clean ROM, drag and drop. Works on any OS
-Built in NoPass
-Automatically detect save type
-Save directly to MicroSD card, not to onboard chip
-Supports Moonshell and other homebrew.
-User friendly skinnable interface. Touchscreen or button operation
-Supports rumble pak and memory pak
-Supports the WiFi game, DS Rumble Pak, DS Browser
-Supports changes of the background of Operation Interface
-Support Skin DIY by setting background and font colors on Main Menu and Game Menu manually and automatically
-Supports 4-scale-lightness adjustment ( DS Lite only )
-Supports the Soft Reset.
-moonshell 2.02 support Software Reset function( Press START key back to the R4 menu)

No.5 iSmart MM
Features:
* No conversion needed, hardware decoding.
* Supported video formats: RMVB,RM,AVI,FLV,MPG,WMV,MOV,3GP
* Resolution: 640×480
* Display mode: Original mode,standard mode,full screen display
* Supported formats:MP3,WMA,APE,FLAC,WAV,AAC,OGG,RA,M4A
* Play Mode: Sequence, Random, Single, Single Loop, All Loop play.
* Four Slots Real Time Save, Real Time Guide (text and BMP image) and Real Time Cheat (.DAT format).
* MicroSD supports up to 32 GB.
* Multiple languages: English, Traditional and Simplified Chinese, French, Italian, German, Spanish and Korean)
* Built-in NDS/GBA emulator
* Hardware supports Slow Motion (4 speeds)
* Anti-Piracy, no patches needed for anti-piracy built-in games
* Built-in DLDI homebrew support