What sizes/types of flies will you generally tie? Most quality vises can handle a fair range of sizes, but hooks at the extremes of the size spectrum may be challenging for some jaws and vise designs.
What vises have you tied on? What are you presently using? And what features do you wish to gain with the new vise?
Folks will have differing opinions on "top shelf." It may help to quantify this with a min/max range of expense.