I dont use faceplates, so I cannot say if it is easier to work with UDTs for faceplates.
However, it is generally better to use a global DB than an instance-DB for data that has to be accessed outside the FB or FC. So I would use a global DB and UDTs for the data that has to be accessed from the HMI. All other data (that isnt to be acessed by the HMI or from other blocks outside the FB) can better be packed inside the FBs instance. In that way if you need to you can change the declaration part of the FB without it affecting the HMI.