Warning: Do not buy a new iPad!
At least until Apple likely announces new models in March. New models have new features and current models drop in price. Last fall when Apple would have normally rolled out a new iPad, they came out with the Pro model. Since that is a product in its own right, the standard iPad has not had an upgrade for a year and a half. A spring model seems likely and it is also possible they will switch to an 18 month schedule. The current models are very powerful and most future improvements will come in the operating system as well as the apps - annual upgrades may be a thing of the past.
And if you're a serious iPad user, you should consider upgrading if you have an earlier model. The most recent iPad Air models are much faster than the first four versions - a trend likely to continue with the coming Air 3 or whatever it's called.