If you want to look at rational and irrational, many people consider Ralph and Piggy to be the personification of rationality in the book, representing the ideas of society, rules, order, etc. Their main enemy is Jack as he tries to embrace chaos and the pursuit of almost hedonistic pleasure. He urges the boys to think only of their hunger, their desire to hunt, to take pleasure in the hunt and the kill.
For individual versus collective you might look closely at Simon. He is the only boy to realize where the real beast is and as he tries to share this knowledge with the group, they attack and kill him, fearing any individual intruder.