Tense Question (as in Grammar, not emotion lol)

I've been an English teacher for 25 years and have mainly written poetry in times of strife, and have a few chapters written of a fictional memoir, but it never came to anything. I have always dreamt of one day writing something, but until a few months ago, it was just a thought in the back of my mind. Now I'm 6 chapters into a fiction novel (reading fantasy over the last year after being a memoir, day-to-day fiction, and non-fiction reader for my entire life has inspired me tremendously) and I keep re-reading and changing things as I go, which is fine. Today, as I reread, I wondered whether it is better to use present or past tense when writing in third person. Anyone have any thoughts on that? If so, please let me know your why. Thanks!