tl;dr
Assuming the question is strictly about performance:
- v-show: expensive initial load, cheap toggling,
- v-if: cheap initial load, expensive toggling.
Evan You provided a more in depth answer at VueJS Forum
v-show always compiles and renders everything – it simply adds the “display: none” style to the element. It has a higher initial load cost, but toggling is very cheap.
Incomparison, v-if is truely conditional: it is lazy, so if its initial condition is false, it won’t even do anything. This can be good for initial load time. When the condition is true, v-if will then compile and render its content. Toggling a v-if block actually tearsdown everything inside it, e.g. Components inside v-if are acually destroyed and re-created when toggled, so toggling a huge v-if block can be more expensive than v-show.