Need help on choosing a gemstone

Hi everyone,
A total noob here. Wanted to seek some advice and perspectives. Am thinking of customizing a ring for my wife for our 20th Anniversary. It could also be something she can pass on to our daughter in future. I’m narrowing down to the following stones:

1) Diamond
2) Peridot (Her birthstone)
3) Spinel (also her birthstone)

Can I solicit some views and advice on what should I take into consideration when deciding between the three stones above. Any views is greatly appreciated.