Nowadays, theres a few different options out there. You got different metals and sizes. Each have advantages and disadvantages to them but ultimately I always leave it up to the client.
Stainless Steel- Strongest material out there and will last longer than any other metal. Since there is more involved in the installation expect to pay a bit more. Also, it does seem to add more fret noise and treble to the overall sound.
18% Nickel/silver- The traditional and industry standard. Comes in a variety of sizes and shapes. Easy to work with (compared to the other stuff) but wont last as long (compared to the other stuff).
Cryowire- Nickel frets that have undergone deep freezing treatment in order to make them tougher. Expect to pay an upcharge and they do have limited sizes available.
Gold Evo Wire- Evo gold fretwire is a copper alloy and looks gold. Great if you are allergic to nickel (more people than you’d think). Its pretty tough and durable if stainless isn’t your jam. Some people cant stand the look of gold though.