Good morning Zepheus, the key difference between the two is breath is a ranged attack.. sadly its been nerfed a few times since it landed in pub 97 because of PvP... so it has somewhat of a cooldown and limited range and will only effect things your pet has direct agro with now... V, Bite is a melee cleve aoe poison that will hit everything within 6 in game steps of your pet .. if its aggroed or not...... it tends to proc a lot more then breath these days and I find it to be more effective since the countless nerfs to breath.. .. but depending on the build ya wish to make I would make a copy of the pet to test and try both and see which one fits your plat style better.... Hope this helps , mate.. =^-^=