[Praedos] (and also [Innodem]) are the two best quality of life combo statsticks for [Gara] because you can build x12 combo extremely quickly and then passively maintain combo without having to enter melee and attack. This is due to the Universal Readiness perk on 5th evolution, which means simply shooting your primary (which helps proc Arcane Blade Charger) and picking up ammo will constrant refresh/build combo.
Riven:
Positives: Damage, Any Element, Puncture (Slash is ok but not preferred)
Negatives: anything except the above and attack speed/range
Evolutions:
Evo 2 : Drifting Grace +20% Sprint Speed and Slide
Evo 3 : Shockwave Synergy Gain 4 combo on slam
Evo 4 : Evolved Ascension +30% parkour velocity
Evo 5 : Universal Readiness Collecting Ammo grants 5 combo counter