Even though the Sixers are athletic, I'd rather see the C's play them in the first round. The Bulls are inexperimented but have a lot of talent on their team, and a pretty good rotation. Plus, they have two big scorers (Gordon and Salmons) who can erupt for some games in a series.
I agree with you, the Sixers are the weakest team of the East and the Celtics would beat them easily but they are not to be underrated too.