Glass over the screen that protects your eyes? Say wut?
The glass just creates glare, in reality, it hurts your eyes while using it outdoors then helps your eyes. The iMac is a far more powerful system then the 13" MBP but if you want portability, go with the MBP.
What are you going to be doing with it? What programs are you wanting to run? Do you need portability? Personally, if I was in HS still (and not having a 25th reunion this summer!) I would get a low end iMac an an iPad.
The iMac to do more processor intensive stuff like videos, pics, projects and papers.
Then I would use the iPad for surfing, facebook, email, etc.
To buy both would be the about same price as the MBP
I would get a laptop. You are soon heading to college where a laptop is almost a must (at least it's a nice extra) so you may regret it if you go for the iMac. You can always get a external monitor, mouse and KB and hook your MBP to the monitor and use it as a desktop