I was a big SFZ user and promoter for years (decades?) even in the early days of this forum. However, I have quickly moved to the Decent Sampler format.
The main reasons are:
1. The ability to create a beautiful custom GUI for your samplepack. Plogue, the maker of Sforzando SFZ player, usually charges developers for the ability to create custom interfaces. sfizz, the other main SFZ player is open source, and currently it lets you stick a photo on the front, but clearly it was not designed to be beautiful. Also, the SFZ specification has little in the way of GUI codes other than image=path-to-image.
2. Random Robin – both formats allow for round robins, but random robins are a hassle in SFZ.
3. Packaging – you can zip the whole package of files into one file and unzip it to edit very easily.
On the other hand SFZ has a long history, and therefore more supported features (many related to synthesis).
Check out the tutorial section of sfzformat.com to see if those features are important to you.