Doesnt really matter who gets steal in the active party to begin with but I always build that person up with luck and dexterity, and give them deathblow too. Using chocobo lure materia and luck plus materia helps a lot, as well as all the luck sources you can find!
And using the curse ring at any point is a REALLY bad idea I cant think of a single oppurtunity where its useful. Its just for people who are mega smart and can think a way round all the disadvantages and status ailments that it gives the character who bears it!