Sysnand because it makes sense... Think about it... The simple fact is, if you are running arm9 then you are now at the mercy of the firm0 and firm1 partitions. If these two system partitions corrupt while running sysnand or emunand....Brick!
Where in this explanation does emunand offer any more protection? You have already tampered with the integrity of firm0 and firm1 partitions, emunand can't save you now anymore than sysnand at this point! Plus a big benefit that seems to be overlooked here to arm9 + sysnand, increasing memory card life! Excessive writes to any mem card like this (treated as a nand) will significantly reduce life expectancy of your micro SD card life.
And one other benefit, you only have to maintain 1gig backups of ctrnand_sys as there is no point in keeping multiple backups of the other partitions because multiple restore to these partitions are unnecessary (again, preserving the life of the other partitions by avoiding unnecessary writes)
Lastly, I think, the safest thing to do with an arm9 system, either get rid of emunand all together or keep it but keep it running at a current version. That way you need not worry about accidental updates (for those who are super paranoid) that's what I did, and now if have a stealth mode I can toggle
