Leveling build for new guardian
I leveled guardian up through map/world completion. I essentially maxed out the power trait line followed by precision, and lastly toughness. Each time I unlocked a new tier for traits I would just rinse and repeat.
In my personal experience leveling characters, I haven’t noticed the effectiveness of any builds until you get closer to 80. Berserker is the meta for PvE at the moment and was what I did with guardian. You have enough innate survivability that you should have it easier than most classes.