What is the best way to set up Gmail on IPad?
Setting up via Exchange is my preferred iOS Gmail setup. In earlier iOS versions (I think 3.0) you were limited to one Exchange account. So in my case, that was reserved for my work email. But once that limitation was lifted, I switched Gmail to Exchange and have been quite happy with it. 

You get push email, which is the main benefit, but you also get push contact/calendar updates. Depending on if you use Google calendar as your main calendar, push calendar updates and invites can be a huge help to managing one's day. 

If you decide you don't need push while using Exchange (or ActiveSync, which is the specific mobile protocol used by Exchange and Google), disabling push is quick and simple. Setting up via ActiveSync also saves a few steps in that you don't have to link your calendar and contacts manually.  So I say go for Exchange, even if you don't use push. But it's not a huge deal either way, and as it's so easy to add/remove accounts on iOS, if you pick one and don't like how it works out, you can always switch to the other with minimal effort.