I agree with the others

I leveled my toon before 5.0, so I really don't know if something is changed a lot BUT hellion is the tank pet and you'll use it only during leveling. Unless having Fountain of Death to change builds on desire (hellion is useful only against warriors in endgame), at endgame hellion is totally useless. Endgame pet is only Lurker or Cadaver, depending on what kind of build you have.
I found some problems between 55 and 60lv with hellion's aggro, but I was full legendary lv55 equip with blue glyphs and 5/4 runes. Mabye a toon with no old endgame equip and no upgraded glyphs avoids it.
I find Reeah19's build nice, it's similar to mine BUT I'm not sure about Determination rubies, because imo it's quite useless using dots and you need to be focused (if hellion maintain aggro, you won't be focused at all), because if you cast a spell with a (example) 50% DET and then you reach 100%, your dots will be still based on the 50%, and viceversa.
So it's more useful with attack spell like vampirism or acid bolt, unless you use it only when it reach an high %
Or at least, someone explained it to me in this way