I have been a Hilton Gold or Diamond for many years and last year was making a lot more worldwide trips and saw that Starward had better standard hotels in more locations than they do in the UK and europe so asked SPG to match my Diamond Status. (I was SPG gold already) They did. After a few stays I can along the following pros and cons:

SPG always let me in the exec lounge which is a great benifit. Hilton do only if in an exec room.

Although SPG promis Suite upgrades I never ever got one. Hilton dont offer this benifit officially but I often get suite upgrades.

SPG upgrades were generaly poor - mostly to a room with a view.

SPG offer a nice welcom gift which Hilton do not.

4pm check out (is this still an official benifit?) is brilliant and a real plus that Hilton do not offer. Hilton usually charge after 2pm maximum.

Hilton points are easier to earn and cheaper and eaier to use. This is a big plus for Hilton.

The ability to use points for suite upgrades is very good for SPG although they are a lot of points for suites.

Hilton have a lot more hotels throughout the world. Starward properties can be of a higher standard though.

There are probably a few points i missed but these are the matters that were important to me and that I noticed. In the end I had to make a choice as I dont have enough hotel stays to keep both status' going. In the end I chose Hilton. I find their customer service generaly good na dmostly get good treatment as a diamond. At Hilton I get a lot more points for each £ I spend and there are often offers to boost it. I now have some starward points which I am finding very difficult to spend because of the high season.