~Now this guide is only based from a lv 37 mercs point of view. These are my OPINIONS.
I’ll start with a image of my stats and skills. (Stats are of me naked)

Now after being level 37 and mixing the stats up a little bit at lower levels, Dex, Int, Will did NOT effect me enough to be worth adding more into. And at level 37 (20 will) does nothing for my crit rate. I rarely crit now.
Break down of Passive Skills:
Stone Skin @ (9) 381 defense
Composure @ (7) 172 hit rate
Heart of Steel @ (3) 529 health points
Two handed Mastery @ (4) 99 max damage
Aggression @ (4) 15% increased damage. (Lv4 is max)
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My thoughts on the passive skills:
Stone skin: not as useful at higher levels. A friend has level 3 stone skin and while we wear the same armor, he only takes 50 extra damage hit
Composure: Extremely useful, possibly not needed to max out asap. 5 to 7 will carry a long way it seems.
Heart of Steel: Not a total waste of points ~200 hp each skill point into it. Very useful if going a (5:1 Str/Con build.)
Two Handed Mastery: So far seems like a worthy investment. Need more research to compare if points would be better spend in Berserk.
Aggression: Having it being based on a percentage it seems like this is MOST useful at high level towards end game level.
(Gladiator Passive-Deathblow training): This skill increases only the damage dealt by critical hits. Unless you are a will build. This looks like trash.
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There are 19 skills that a gladiator can utilize (without switching to a onehand and shield)
5 are passive skills. Only 4 I see as useful right now. @level 79(Current max level) you will have 79 skill points. 17 Need to be spent to have the useful skills. 17+48-5(Number of passives already added)(Death Blow Training and Balance Up do not look necessary) 48 Will be used to max out the passives listed. This utilizes 60 of your 79 skill points. This will give you 14 points to throw around for leveling your final level skills. (Lightning Recall, Blood Fury, Tornado Slash, Gale Smash.
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General advice for stats. Str/Con/Wis (20 wis allows me to to use Upper Strike every mob and Gale Strike every Other Two mobs without having to sit down until my hp is depleted beyond "safety level" ~15%)
*5 is the number of passives already in the equation by number taken to max out passives.

Credits go to Sekia.