nn or 2n2. I think that the n term will grow faster than the 2 term and the n2 will grow faster than the n term, but overall will the n2 exponent cause the second to grow faster.
Let's get ln from both sides:
log (n ^ n) = n log n
log (2 ^ (n ^ 2)) = n ^ 2
Obviously n ^ 2 growths faster than n log n. It means that n ^ n growths faster than 2 ^ (n ^ 2).