The advantages of having a longer engagement (over a year) really only occur if you get a jump start on your planning. Having a longer engagement means you can basically have first pick of your favorite vendors, since many popular contractors are booked well in advance. And booking over a year in advance will also allow you to book the venues in the month that you and your fiance desire. Once your vendors are booked, you will have a nice stretch of time in the middle for non-wedding planning free time. You will also have more time to save for a few extras and custom details you may want to add. That being said, you have more time to rethink your options and may end up spending more money to change previous decisions.
A short engagement also means a less time to plan. The two parts, booking and organizing, become condensed into one timeframe. You will generally find yourself concentrated on the four different items that your guests will notice the most. This list includes, the wedding gown, food, entertainment and decorations. Many smaller customized details will be left out . (ie monogrammed hand towels - that honestly your guest won't remember anyway.) And since these extra details are generally left out, this will help save on your budget (or allow you to deligate that money to another area). If you choose a shorter engagement, it is very important to write a detailed list of all the components that are most important to your wedding day. Start with the absolute must-haves and work your way down to the little extras. Be realistic on your timeframe & always overestimate the time it takes to have that task completed. IE Do you really have enough time to have a custom gown made?
So whichever you & your fiance choose, remember to stick to your budget, be realistic on the time frame (by over estimating on both) Your engagement should be an exciting time and not a stressful one. So if finishing school exams collides with the wedding day then it may be best to push the date back. Or if you just can't wait to be married to your best friend - then go for it! And remember have fun!