Start new application in Ionic 4 beta or Ionic 3 stable?

Hi, I gonna start develop new app in two weeks to my client
It’s very huge and important app
It will take 2 months of work for two developers

Ionic team, do you recommend to start from develop it with Ionic 4 or Ionic 3?

Current Ionic version.

Ionic 4 is not in beta yet. It will also be a pretty simple upgrade, compare to the switch from v2 to v3.