if you are just making screen casts, a macbook air is good enough.
if you're making videos from a vacation or an event, then you would probably want to get the pro.
Quicktime will allow you to edit your videos minimally for the web and is free with all macs.
iMovie is downloadable in the app store when you get your mac.
These applications should run just fine on both computers however it depends on rendering time and storage space. if you want to render long videos in HD you're going to want a Pro, if you're rendering short how to videos, then you could get away with getting an air and then backing things up in the cloud or on a server or on an external hard drive.
The air is the replacement for a macbook (white/black body and for a short time aluminum). It is nice for it's slim portability and built in SSD.
you can get better performance and also an SSD to run your os and it would be similar to the air.
Why are you on the fence about this? if you are constantly moving around with your computer from place to place, constantly opening and closing it and throwing it in your messenger bag and treat it like an iPad, then get the air, you'll have more fun with it.
if you're main focus is being able to make these videos, any videos, no matter the length of time then get a pro and get the best pro you can.
All of this is moot because I would also wait a little bit to get your computer. 😉 😉
@sig I like to humur the obvious sometimes. Sometimes people find it more helpful.