When it comes to law professors, Harvard usually grabs all the attention: Senator Elizabeth Warren , omni-presence Alan Dershowitz , Supreme Court justice Elena Kagan , the fictional Charles W. Kingsfield Jr. (played by John Houseman in 1973’s “The Paper Chase”), the list goes on. But it is Boston University School of Law that nabbed the best professors ranking in the Princeton Review’s 2014 list. “This marks the seventh consecutive year that BU Law has ranked among the top three for best professors, earning the number one spot a dominant five times since . . . the 2008 edition,” BU crowed, understandably. As for famous profs? The “rock star,” said Dean Maureen O’Rourke , is contracts professor Mark Pettit , known as the “singing professor” for his love of crooning legal spoofs of hit songs.