This.
If you want to buy an Air-size iPad, wait for the march event.
If you want the Pro-size, nobody but Apple will know when the next update is going to happen. It's highly unlikely to update a product which is only 4-5 months old. It's more likely to have a one, or even a two year cycle.
If you can wait that long, then wait. But then again, if the new update comes out, there will be a newer one in the following 2 years....
Sure, but you never know anyway. If you can wait because something new will be coming, two things can be said: 1) you dont need the device, so you are getting for pure consumism; 2) you will never get anything as there will always be something new and better around the corner. Therefore, if you really need the device now, get it now!