I think a lengthy lease depends on your personal circumstances, in our case, the Office Manager gave me all the different rates for different lease periods, the least expensive was a 16 month obviously, so I negotiated $100 off that for an 18 month...
The reason being, we love our little Townhouse, we love the location - only 1.8 miles from work, a 6 minute commute- close to the Bike Trail and ultra quiet.
Plus we know all the maintenance Guys, a great crew and very friendly...we've already been here for 2 years, time flies!!
So for us it works.
I highly advise you to negotiate!!
On the other Paw, an 18 mth lease is pretty rediculous because I never know where I'll be from one week to the next the way things are going at work, but that's OK, 95% of the population is in the same position, I'm prepared.