In a way the source of Anubis' power came from his recent history, and therefore his access to all sorts of super technology which gave him at least temporary advantages. However, since he was, at the heart of it, a Goa'uld he suffered all their genetic weaknesses.
What the new villains sound more like (i.e. the ones from Atlantic, who presumably find a way back into our galaxy) are the Shadows from B5...
I suppose if you wanted to determine what properties to have you would want a foe never to meet, it would include: technological advantage, superior numbers, intelligence, cunning, individual self-sacrifice for the good of the race, speed, agression, and even worse, no reason for the attack (ie that can't be bought off by finding an alternative to their "need" to attack us). If you were to add in hoprribly ugly, smelly, non-corporeal might be a challenge, and so on...