Ok;
In group F, Brazil are going through for sure.
In group E, Italy are going through.
This leaves three teams in each group competing for one other place. Now, in group F, those teams are Croatia - an excellent team and Australia, one of the rated underdogs of the tournament.
In group E, there is the US (who had suffered the biggest defeat of the tournament before Ukraine today, and who basically have no chance of winning the cup) and the Czech Rep, a team who are rated highly on the FIFA rankings (not that this matters much) and have some class in their team. I think we can disregard both Ghana and Japan as having much chance.
Thus, the competition for second place is tougher in group F.
Thus, group F is harder than group E.
Now, I don't think we need any explaination for C being tougher than E...
edit; Bryan you might pinch one (a goal) against Ghana, but don't be too optimistic.