I don't have a very high opinion of the seven sins, or sins of any kind. They'r outdated, archaic, and their original versions are irrelevant today (Religiously, Pride has more to do with the sin of being self-confident and independent enough to have no need for your god).
But with more modern interpretations, and for laffs, my three main sins are:
Sloth - It has affected my schoolwork, and is currently contributing to certain anxiety (University) and boredom (too lazy to do anything useful, eventually gets to you).
Greed - I enjoy my modern privileges, and the materialistic "stuff" available to me while i live with my parents (In the process of moving out. Don'th ave that much money myself). I also enjoy collecting stuff, including Magic: The Gathering, Mangas, books, and of course video games (Trying to limit myself to only buying Guild Wars 2 and Total War: Shogun 2, but Dragon Age 2 and Arkham Asylum look awesome as well). It costs money, which i don't have much of.
Lust - After 20 years and still no relationship in sight, the need to satisfy some basic human needs are starting to surface.