m.scott peck derails laziness as the lowest of sins. he reasons that one must continue to strive, to fight against atrophy and decay and to do otherwise is death and sin.
others, i think, c.s. lewis, inclined that pride is one of the worst for its impediment. specifically, if one feels themselves better than their fellow man and even God, well it makes communing kind of difficult.
c. stanley discusses blaspheming the Holy Spirit as essentially ignoring God's call to come to Him. a certain pinnacle of sin.
i sometimes think my dad holds smoking as one of the worst sins. whenever he mentions that someone is smoking, he gets an extremely disdained look. He'll be saying, "i saw her out back smoking a cigarette", but his face is saying, "i saw her out back rolling in her own feces." he'll witness to these heathens that they ought not engage in such sin, for their health.
i know a foreign lady and her american lover who think that eating meat is the deadliest of sins. they consider it so for what it does to the human body, the environment, and i suspect most importantly what it does to those poor lil animals. they are fabulous proselytisers and miss no opportunity to preach the figurative fire and brimstone about thier favorite sin.
on a more global scale, the voodoo culture of haiti note that disloyalty and ill-will towards ones family is of the most abominable (at least according to "the serpent and the rainbow"). so horrible is the sin that you may be justly turned into a zombie for the crime.
for some people, sexual sins seem always to be the worst, most heinous of sins. you know, gay sex, pre-marital sex, masturbation, what-not. i wont prolong myself here (pun intended).
i dont know if God weighs sin the way we do. one being worse than another. i may despise one more than another, but maybe thats more about how i was raised or the pain that particular sin caused me or the sin witin me seething beneath the surface.
Jesus seemed to even the playing field of sin when he noted that lusting after another man's wife is as bad as having adultery. Also he tended to focus less on carnal sins and more on those who elevated themselves above other sinners.
i think any and all sin is in essence spiritual disease. some may have differerent symptomotology than others, and a different short term prognosis, but all have the same long-term fatal prognosis.