I decided to concentrate on the half marathon (and 1ok's). Having completed the marathon distance, it was very fulfilling but the training was time consuming and the recovery time limited the number of marathons I could do per year especially since you lose 3-4 months living in a region with a real winter and snow.
Here's the reasons why I decided to concentrate on the half marathon instead of marathons and ultra distances:
1. Half marathon is still challenging and you can concentrate on more speed work.
2. You don't lose entire weekends with really long runs as there is no need for a 18-22 mile run.
3. You finish the half marathon and feel fine (you can still go dancing that night).
4. If you are unhappy with your finish time, you can enter another half marathon race within weeks/months.
5. 10-15 mile long runs are all you need (less than 2 hrs. of running).
6. You don't hit "the wall."
7. I've never had post half marathon depression but I did feel a let down after completing the marathon probably due to all the training required for such an abrupt ending.
8. I've already completed the marathon including a 32 mile run.
There may be a less risk of injury just based on less miles required during training but I'm not sure as other factors weight in to that conclusion including how you train, # of miles, pace, etc.
That's my perspective. To each his/her own.
HHH