There are 2 variations of the deadlift that are best used for strength gains; the conventional deadlift and the sumo deadlift. The romanian or stiff leg deadlift is more of a supplementary exercise. The conventional deadlift is the best option
Barbell straight back stiff leg deadlift. An isolation exercise. Synergistic muscles: Hamstrings (Biceps Femoris, Semimembranosus, Semitendinosus) and Adductor Magnus. Important stabilizers: Erector Spinae.