I find that as siegfried playing against NM, many of his stances are punishable to the extreme, and because of that, I find myself greatly limiting my move list against him. Maybe I'm wrong on this but playing a safe game waiting for punishments (and he's got good ones too) seems to work well for me. If i try going all out aggressive I get my A$$ kicked.
On the other hand I find Sieg much easier to win against the short reach, faster characters than NM.
Overall, I would have to disagree with the idea that Sieg is easier to use. NM has less moves, less stances and is slightly less punishable. Sure Sieg's moves are easy in terms of button inputs, but he's also harder because of his MANY options that he has. Not to mention NM seems like he's just a pinch faster overall. It is easier to mix things up with Sieg, but NM's mixups aren't too shabby either.
IMHO, NM is THE easiest character to use in the game. His moves are simple, straight forward, and devastating. His juggles and combos are also extremely simple. When using NM, I never find myself thinking "okay what do I do now?" It's pretty easy to figure out what to do with NM. If I use Sieg, even tho its still easy, there are those, "oh crap half my moves aren't working, WTF am I supposed to do now?".
Slightly off topic: Give NM back his 2A From SC3!! It's the same one Sieg has.