@kelbot can't say I've tried playing video on it; my phone kinda already fulfills that purpose for me. :)
Tbh, I don't have much experience with various loaders and flashcarts. I got the #Acekard2i #flashcart years ago since that one was at the time one that was well-developed, supported and quite cheap. It's still running (a rather old version of) #AceKard All In One (#AKAIO) because it seemed to be the most popular and actively developed loader.
https://wiki.gbatemp.net/wiki/AKAIO
http://www.akaio.net
AKAIO - WikiTemp, the GBAtemp wiki

@kelbot
#GBATemp is overall a decent resource for info, though I must admit I haven't really looked into #NDS #homebrew for quite some time.
#DSorganize is a nice #PDA-like organiser util with a file browser (which will play audio files), todo list, calendar, day planner, address list, scribble pad, and even web browser and IRC modules, and a homebrew database.
There are also various emulators, though IIRC the lower resolution compared to a TV, means you'll miss some lines on e.g. #SNES games.