If you're talking about past/present, then I agree with Lisa - it's an important decision based on the genre of your work and how you want it to feel.
However, if you're talking about first and third person, it's another important decision that revolves around what kind of story you're trying to tell and how you want it to feel. While first person allows you to develop a character strongly and tell a deeply personal story that lets the reader connect to the main character, it limits you in the way that you can only tell that one person's thoughts, and are limited to telling the story through their eyes only - meaning they need to be present for all important events. Third person allows you to tell a more complex story and show the emotions and thoughts of multiple characters, as well as have scenes with some characters and not others. This allows for a good amount of freedom when writing and is useful for developing characters that the main character isn't close with. At the same time, it does keep the reader in a position where they're on the sidelines watching, as opposed to being right in the action.
The decision is up to you for both, but I hope this helps in case you meant POV instead of tense.