You're gonna hear the same from me like from many others who may post, but I'm gonna post the reasons anyway.
Original R4DS (1:1 reproduction) is definitely a worthwhile flashcart for any DS Lite users on a budget, the flashcart itself can be picked up for about $3-6 and it can use up to 2gb microSD cards, and run the popular Wood firmware.
For that same reason, R4i Gold/3DS with its added 3DS/DSi support and SDHC support, being able to use Wood R4 firmware makes it highly attractive as well.
Acekard 2i is a similar flashcart with reliable firmware updates and the famous AKAIO firmware, with excellent compatibility and runs software both homebrew and commercial impeccably. I can remember bygone days where some games may run, but they had noticable jarring pauses in games like Pokémon Platinum when entering battles or towns. Issues being resolved like this is a testament to the accomplished AKAIO firmware.
And finally there's the Supercard DSTwo, the premium of DS flashcarts. A bit more costly around the $35 dollar range, these babies sport an internal processor that enables it to do some revolutionary things like playing video formats without the need to convert (like with Moonshell), and emulate both GBA and SNES titles.
My favourite features are part of the DS rom compatibility however, its anti-piracy circumvention is unbeaten in the flashcart scene and almost every new scene release has worked on day one. There has only been a very few games that have needed patching or updating of the firmware.
On top of that, it has the best real-time menu of any flashcart, with four save-state slots of great reliability, the ability to load an unlimited number of .txt or .bmp files as game guides, the ability to toggle cheat codes without interrupting the game, and other small things like soft-reset or memory hacking.
It really is the dream flashcart.
On that last note I need to state why I do not recommend the CycloDS iEvolution. Sadly this is a flashcart past its prime, whilst it was a worthy improvement over the original R4DS at its inception, before the age of the DSi, its feature set has not been improved upon with its DSi incarnation.
The operating system has not been significantly improved upon from its original version, only the addition of a touchy DSi-mode. Whilst it allows DSi-enhanced titles to be run in DSi-mode (such as pokémon black/white), as well as homebrew and non-DSi enhanced titles, these games tend to run unreliably, with bugs or freezes.
The real-time menu, which CycloDS brought first to the DS scene, is pitiful compared to the DSTwo. It is very slow to actually display when summoned, and offers only one real-time save (which must be prepared before loading the ROM), only one .txt file that does not even support word-wrap, and does not take advantage of touch-screen capabilities.
On top of all that, they CycloDS team seemed to have disbanded, firmware updates that improve game release compatibility do not exist with no alternative firmwares.
I truly loved the original CycloDS at its prime, the same can be said of the original R4DS, but it no longer satisfies the needs of an active DS player.
