The two seem rather odd choices for a compare and contrast paper, as they have little in common. Ed Abbey was a writer and environmental activist, known for his advocacy of direct action to defend the western wilderness. He was very much an outsider, a lone, rugged individualist in love with nature and solitude, deeply distrustful of politics and of Washington.
Hilary Clinton is a lawyer and Senator from New York State and former Secretary of State, currently seeking nomination as the Democratic candidate for President. Although she shares in common with Abbey a desire to protect National Parks and wilderness areas, her positions are much more moderate and expressed more diplomatically.
Before you write a thesis statement, you need some sort of rationale for why you have chosen to compare these two people. Normally, the ideal choices for a compare and contrast paper are figures similar in many respects but differing in some specific area, such as Clinton and Bernie Sanders or Ed Abbey and Wallace Stegner.