For patch 0.26.0.2

Did some testing on the Treants and Flourishing Treants in Glinting Hollow, same amount of kills each pet type with both Untamed Spirit and Guardian Spirit, no other buffs or auras. I simply used a digital stopwatch for time to kill each mob(TTK) and how much health the pet had at the end of fight(estimate %). After collecting all the data, I took the average of each combo(25 kills per combo, a mix of both treant types). All pets were level 60. I chose these treants because the pets could solo them without interference from me, but still conned dark green. Remaining health error margin unknown due to eyeballing it, TTK error margin +-1s.

Damage Pet

Untamed TTK average of 1:08 and 69% health left
Guardian TTK average of 1:38 and 61% health left

Balanced Pet

Untamed TKK average of 1:12 and 61% health left
Guardian TTK average of 1:38 and 61% health left

Tank Pet

Untamed TTK average of 1:15 and 58% health left
Guardian TTK average of 1:59 and 62% health left

Other random info:

+24wis at 60 = 1 extra heal, and 1 wis = 1.3 additional health per tick. So +24wis at 60 will add 31 extra health per tick to your pet heal.
Aquatic Affinity lets you hold your breath for 14 minutes.
Running from the top of the Penshaw Village lifts to Night Harbor using only Prowler's Instinct + Hunter's Chase takes 25mins to zone in, 28mins and 27secs to reach the door of West Bank, the Boat takes 30 minutes from Penshaw to Night Harbor.
Sneak effect from Prowler's Instinct works while under the effect of other movement speed effects like Speed of the Wild, the speed effect does not stack. The sneak effect also allows you to pass undetected while behind enemy NPCs that can see invis.
Cooked meat sates your pet longer than raw meat, haven't tested it extensively, but cooked can last twice as long as raw.

Two-Handed weapon vs Dual Wield

Rusty Iron Maul 2h 18/52 versus x2Rusty Steel Shortswords 9/26 to test 2h Chop and dual wield Maul on the same treants I used for testing pets. The weapons have the exact same ratio(.3461) I used the same pet with Guardian Spirit(to avoid Rip proc rng) and Predatory Instinct active for every kill using either Chop or Maul and no other abilities, all melee skills maxed. I killed 25 Flourishing Treants and 25 Treants for both 2h and dual wield and took the average TTK. Here are the results:

2h Rusty Iron Maul 18/52

TTK using Chop vs 25 Flourishing Treants + 25 Treants: 50 seconds average

Dual Wielding 1h Rusty Steel Shortswords 9/26

TTK using Maul vs 25 Flourishing Treants + 25 Treants: 60 seconds average

Not testing dual wield Chop since it will supposedly not work in the future, 2h only abilities were not coded in for this patch and Chop was intended as a 2h only ability. The crit effect from Chop currently doesn't scale since your pet doesn't scale, this could lead to dual wield Maul with high end weapons surpassing 2h chop due to auto attack damage being able to scale.