Hands down DIY!! Only way I would have someone else do it, is if The money didn't matter, I didn't realistically have the time, and if I didn't have any mechanical skills.
DIY Pro's
You get to know your car
Sense of accomplishment
Save Big $$$
Make sure its done right (no cutting corners)
It's easier the second time!!
You Amass a whole new tool collection
You can make a lot of new friends, like on here
DIY Con's
You get dirty
You can get frustrated
You could screw something bigger up
You could injure yourself
Could be a mess on your garage floor