Both are so called power symbols (or power ports or power labels depending on the source you read)
There is not really one “correct” shape. There are many standards bodies who defined such shapes in the past. And there is not even a guarantee that shapes that are used are really part of an official standard. (Sometimes tools just define something without waiting for the standards body to catch up.)
The right symbol looks like how VDD is represented in at least cadence. The left one is the standard VDD symbol shape in kicad (and i think eagle as well)
So in the end it is up to your preference (or your target audiences).
Typically power symbols are made such that they do not have a representation on the PCB or in the BOM.
What you really need to worry about is how kicad defines the netname. This is not done via the value field (or symbol name) but via the name of the hidden power input pin. For making custom symbols read Tutorial: How to make a symbol (KiCad v5.1.x) - #7 by Rene_Poschl (last section)