Joe:
I’m a long time Apple user. Heavy (mostly internet based) research, writing, parts listing, drawing, picture manipulation and document production. I also do quite a bit of MS PC based programming for automation devices (PLCs & Smart Relays) that we design into products. All computer work is done on my two MacBooks. The MacBooks are treated as portable high performance workstations, but when in the office they are usually hooked to external keyboards, mice, hard drives, and other accessories. They are also both equipped with Windows XP in order to accommodate industrial tools that are not Mac compatible. Most of the stuff I design is used in MS PC environments. I really operate in the best of both the Mac and the MS PC world!
My (generally computer averse) wife has an iPad which she mostly uses as a replacement for her paper copy birding field guides and for occasionally reading internet content. Virtually no typing done there.
As to your stated potential choices: Recognize that the iPad is NOT a computer. It is a really great device when used for its intended applications which include light email reading / text generation, picture viewing, and the above mentioned document access. Before you buy one, try writing and (especially) editing an article on the virtual keyboard. I put it as just slightly better than no keyboard at all! It might just be me, but I don’t even like typing and navigating on the keyboards / touch pads that are on my MacBooks, thus the external keyboards and mice. The iPad way less so! And, virtually everything that you might want to do to make the iPad more like a computer requires some kind of extra adapter along with the external device, thus making it much less portable. Again, it is a great device, but it is definitely not a computer.
The MacBook Air is really a highly portable 100% solid state laptop computer. The main things that differentiate it from other laptops are the lack of multiple hard wired interfaces and the extremely small / lightweight ergonomic design. A truly portable machine with all the capabilities of a computer. The latest versions come in two screen sizes, employ faster processors and solid state memory, and have backlighted keyboards. The WiFi interface is really all that is needed for most operations, but there are also two USB ports that can be used for keyboard, mouse and backup hard drive connections.
As to terminology, the MacBook Air is a “notebook computer.” The iPad is an “iPad.” Note the lack of the word computer in the iPad’s (and similar pad device) descriptions.
Just my personal opinions. Your mileage may vary!!
Happy RRing,
Jerry