Curious to see EZFlash mentioned in such a discussion. Most that would at this point would be more concerned with the EZFlash 3 in 1 (allows you to play GBA games in the setup natively, as opposed to weak emulation or slightly better on enhanced flash carts) which was originally bundled with the EZ5 (and more completely called the EZFlash 5 3 in 1 expansion pack).
The EZ5 has several iterations, ending up with the EZ5i which got updates (unlike some of the older models) until fairly late in the DS lifetime but before DS games stopped (pokemon conquest hit a few days later, pokemon black 2/white 2 some time after that. Many games did not need an update to work but those will, and in the years since there are options). To that end the EZ5i is the latest and with all the shiniest features.
I would generally note the EZ5i as something of a dark horse in western flash cart world (inside China then different matter). It certainly had plenty of shiny features, some even better than what the general king of the hill (the supercard DStwo) sports. Not sure who might be selling them today either -- most would have dropped off after the flash cart killer update on the DSi and 3ds as support similarly went for it (and it would be a while before 3ds and even later for DSi hacks came along to bypass such things from that way).
If doing the general best of list.
Supercard DStwo. Unarguably the best flash cart for the DS. Has loads of nice features (cheat search, guide reader, savestates*), full compatibility, works on DSi and 3ds where others did not... and most interestingly of all for most is it is the main reference for "enhanced flash cart", which is to say it has an extra CPU on board which allows it to play the vast majority of GBA games with a few nice perks over even native hardware options (button remapping and such), play videos encoding in some common formats, have a bunch of emulators do better than native code and even some things that would not even be attempted on baseline DS hardware.
Only downsides are power draw, back when then expense and today good luck finding one at all (you are pretty much limited to hoping someone sells one second hand, if somewhere like here then people will know the worth and that leaves you hoping some clueless mother sells something on facebook or whatever).
*this side of the DS equivalent of
https://gbatemp.net/review/analogue-pocket-gb-gbc-and-gba-handheld-fpga-based-player.2081/ no flash cart savestates are going to be anything like emulator grade -- if nothing else part of the 3d system is write only. Play to it though (go somewhere quiet, test before using in anger, know how to force a redraw of things/restart of music) and you do have savestates you can reliably use as you might in other things.
The Supercard DSone is much the same but does not have the extra CPU and consequently no cheat search, media player beyond baseline DS homebrew and other fancy programs. We were seeing clones appear a while back of various dubious build quality (some were fine, some were not, some could be brought back, some then resorting to buying a stack of them hoping to get a working one out of it as they were going that cheap).
https://gbatemp.net/threads/dsone-clones-appear-to-be-available-for-purchase.586226/
The AK2i is the inheritor of the AKRPG open source firmware (made closed source since then) and thus is the gold standard for flash cart cheat engines, soft reset patches and contributed the vast majority of flash cart fixes you might find. Build quality is not brilliant though so be prepared for a bit of fiddling.
It also morphed into the Wood firmware that powers now the original R4 (don't unless you have one/find one on the street) and a select few other R4_bla_bla_bla things. If you can get an officially blessed by wood R4 clone (not sure what they are these days) that does not feature a time bomb (said R4_bla_bla_bla things often feature kernels that will check the DS system date and refuse to work past a given point, hoping you buy a replacement, others setting dates back or hacking the kernel if they were not able to dodge it in the first place) then you will be able to play basically every game with cheats and soft reset if you want it, which is what most people want -- guides are OK but ultimately a gimmick, cheat search is better in an emulator, and if you have any kind of later device then emulate something on that instead.
The main other thing of note probably then being the M3i real. They fell out of favour a bit after screwing over a prominent homebrew dev (why some tools to use with a 3 in 1 will need a modded version to work on them) but stuck it out for a while and would be a half decent build quality cart that plays pretty much all games with cheat support if it is something you want.
hmmm I'm a terrible pirate lol
