Like any other classes in the game, the stealthers usually have their prime in terms of which RR they're at.
Infiltrator is a strong early RR and gains more strength mid RR and equals out with the others at high RR.
SB is very strong early RR, and gets more challenge the more RR enemies gets. It evens out in the end.
NS has the hardest time early on but scales harder then the others, mid RR it begins to pick up a lot, and is the strongest at high-mid RR but evens out at high RR.
With OF RA's NS was the strongest at high RR, but since all the stealthers now get the same toys it is more based on the core mechanic of their skills. SB has their 2H PA, and LA which always hits with both weapons with unstyled offhand damage, and DW/CD increase the chance to swing offhand the more points added to it. This gives SB the edge early, but as you level up in RR on Alb/Hib your DW/CD naturally increases as well as giving you the chance to dump more points in to it since both Stealth and Envenom requires less skill points to maintain them at 50. Infiltrators gets more spec points, but doesn't get the spells that NS has available for them, so at mid to high RR NS begins to throne due to the fact that they have added damage from instant DD. In the end, they all equal to the same however since there are litte to no uniqueness in their choice of RA's.