I use both hotels out of necessity very often and I would summarise as follows:

Hilton - will upgrade. As a diamond, this is to a suite. The hotel is very old and tired. The rooms are small and uninspiring.

Doubletree- a trendier property with little regard for status. Seems to fill rooms regardless. As a diamond, I have to fight on each arrival for any upgrade or drinks vouchers.

Let us know how you get on!