Technically the answer is 'Most will work' BUT..... (there's always a but..') the current emulators available will NOT use the DSTwo extra Ram/CPU, just the usual DS Ram/CPU (unlike DSTwo GBA Emulator which DOES use the extra memory/CPU), so you will still have the same problems with the emulators that other flashcards have
(Hopefully this will change once the DSTwo 'Software Development Kit' is released)
If you look @ the
DSTwo Plugin list - you'll see a lot of emulators in the list - & on the end of each entry you'll see [DSL/DSi]
If the text is
Black - it hasn't been tested yet
If it is in
Blue - It's been tested on that system & works
It it is in
Red - It's been tested on that system but DIDN'T work
(note however that most of the red 'DSi' were tested on an older Supercard firmware - I should know as I did most of them, but not got round to retrying yet - &
may now work on the newer firmware since the Homebrew compatibility has greatly improved since then )
Incidentally - 'DSL' means DSlite or DSPhat systems, 'DSi' means DSi or DSi XL systems
One thing to note though,
Do not use 'NesDS' on a 'DSiXL'
There has been reports that using this emulator on a DSiXL can damage your screen(s) display -
Exactly HOW it does it no-one really knows, but it's been suggested it could have something to do with NesDS screen refresh rates & how the DSiXL has a 'fixed rate'
Sorry for the long post - but I hope it helps
EDIT: oopss sorry read the bit about the Slot-2 question.... IIRC I think the 3-in-1 is a good bet (I've never had a slot-2 so can't recommend any), but I suggest you search GBATemp to see if there's any better suggestions