That's a pretty difficult question to answer. . Of course, it depends a lot on personal preference, which is so variable.
It also depends on what blank/material you use, which can greatly add to the appeal of the pen, depending on its match to your kit choice.
Bear in mind, also, that not all pen kits come in all plating options. . So what might be a popular pen styling might not have the preferred plating.
My preference for plating would be a combination of Titanium Gold and Black Titanium .... which is probably the most highly priced plating .