I'd mostly book on price. The Hampton is well-run IMO and Gold/Diamond will get a room comparable in size and quality to the HP. Breakfast is comparable as well.
The Hampton is a shorter walk to FRA T2, the HP a shorter walk to the metro station.
Honestly, I don't think the HP is in any way remarkable for its category. So again, I'd choose based on things like price and currently running promos.
Also, I don't recall there being any Globalist benefits during my stays. Done get me wrong, the HP is still a nice to have, especially with it being cat. 1. That can come in handy when prices at the T1 hotels (Hilton/HGI/Marriott/Sheraton) are inflated. But it's cookie cutter and totally unremarkable.