Same here... fruity, tart juices tend to make a coil last way longer for me. My heavy vanilla or heavy sweet juices tend to last half as long.
On my RTA's, like @Walt, I get a month or more out of the coil, but I may have to re-wick it every 7-14 days? A small price to pay for the convenience of a great vape and long lasting coil...
Another thing to consider is the number of tankfulls you're going through, compared to your roommate? Sometimes, when we look at the number of days, we're compare apples to Buicks... If you were a heavy chewer, you may be a heavy vaper... a coil may last you through 10 tanks, but you rip through 10 tanks in 3 days... whereas your roomate may vape a tank a day, thus his coils last 10 days (same 10 tankfulls)?