I've never been loyal to any particular hotel chain, and I haven't stayed in as many hotels as other people in this thread, but please let me give my two cents. Hilton's quality has fallen dramatically over the last 15 to 20 years. 25 years ago, Hilton was my favorite hotel brand. Nowadays, every time I stay at a Hilton I am disappointed. Their properties look very old, basic, and cheap. I get the impression that they have not invested as much in upkeep and modernization as other hotel chains. To give just one example, I fly from Japan to the central US every year, and I have a choice of going through DFW or ORD. One of the reasons I now prefer DFW is that the Grand Hyatt DFW is far superior to the Hilton O'Hare. It's a totally different experience. The Hilton O'Hare just looks tired and depressing.

The one really good thing about Hilton is their app - their online checkin and digital key feature work really well.