I think that atm EOS might have the best or near the best compatibility with new games that need ap patches (in some cases new games that don't work in any other card or that need ap patches work in EOS without needing to apply patches or anything). That happened for example with Shin Megami Persona Strange Journey and Super Robot Wars OG Exceed, that work without patches in EOS and in other cards they needed to wait for a patch/update to be released.
Also since it's one of the few cards with a clean mode some more games that don't work in other cards work in it.
That's the good part. But being honest in some cases when the games do need a patch (like with Pokemon) sometimes the fix takes a bit more than with other cards (but it eventually gets fixed). They might not be the fastest, but they are pretty reliable.
In my tests, the compatibility overall is pretty good, i have a compatibility list here:
http://forum.supercard.sc/thread-5649-1-1.html and right now from 300+ games that i have tested, only 3 have serious problems (and i haven't tested those 3 in EOS SP2, so probably some of them are already fixed, i'll try to test them soon).
Also so far realtime save seems pretty much stable, haven't had problems with it so far, tough i don't really use that function a lot. The same goes with the realtime guide, though this one has some visual problems that need to be fixed, but nothing serious.
But waiting for the DS Two could be a good idea too, since it should come soon and have several advantages over the DS One cards.
Overall i'm pretty happy with my Supercard, and i'm pretty sure that most of the Supercard users are also happy with their cards.