I chose the constitution, though I think, specifically, they hate the bill of rights.
The constitution grants powers to government, which they of course are all for, particularly when its a power they can "grey area" and expand to their hearts content and/or our pocketbooks detriment. The "Interstate Commerce Clause" is one such example.
The bill of rights on the other hand, says "government is forbidden from <insert forbidden exercise of power here>".
That, they can not abide, except when they're using one facet or another, to club their ideological opponents with. They're all for freedom of speech, until someone says something they don't like or disagree with, for example.
CMD