What theory do you think is correct:
Various scholars have proposed that the “sons of God” are either:
(1) fallen angels (cf. À 1:6; some, however, suggest that this contradicts
Mark 12:25, though the reference in Mark is to angels in heaven; see also
2 Pet. 2:4–5;
Jude 5–6); or
(2) tyrannical human judges or kings (in the ungodly line of Lamech, possibly demon-possessed); or
(3) followers of God among the male descendants of Seth (i.e., the godly line of Seth, but who married the ungodly daughters of Cain).
Though it would be difficult to determine which of these three views may be correct, it is clear that the kind of relationship described here involved some form of grievous sexual perversion, wherein the “sons of God” saw and with impunity took any women (“daughters of man”) that they wanted.
The sequence here in
Gen. 6:2 (“saw … attractive [good] … took”) parallels the sequence of the fall in 3:6 (“saw … good … took”). In both cases, something good in God’s creation is used in disobedience and sinful rebellion against God, with tragic consequences. Only Noah stands apart from this sin. (See note on
1 Pet. 3:19.)
(From my ESV Study Bible)