Been thinking about gathering info on the cookie cutter specs available to all the classes.. maybe we can throw it on the wiki or something.
So, it depends on your playstyle. I've said it before, but I consider Fester a gimmick spec. Don't get me wrong, it works great in pug scs, but most of the time you're not going to be able to sit still for 3s when weighing risk/reward. Think BW with less damage output and if you get avoided a lot of your potency is gone. That, to me, is not how SW should be played (I played it for most of rr50 iirc).
But, I'm also rr60 which enables me to get FtW, flank shot, heal debuff, and Powerful Draw. I think you can do this build at 50 if you drop Flanking Shot, but a staple SW build should always include heal debuff and PD. If you're lower than that (<rr50), you might look at getting Fester just because there's not much use in assault atm.
Here is my current build:
RoR.builders - Shadow Warrior
Rotation: dot, heal debuff. I don't start a rotation until heal debuff is on the target (exceptions to this would be if you're chasing or being chased and a slow or *destro trigger warning* rkd is better used first). From there, it's super linear: use rkd, VoN, AP regen, etc as needed. Keep spamming SFA on your target, and pretty much your main job is to make sure your target stays heal debuffed. If you're running in a group, you should be running with a WL, SL, BW, etc.. something that has burst potential so you can keep dealing consistent damage. Obviously you then use Flanking Shot if your target is running from you. It works best around <=30%, or FtW, which deals double damage at <= 20% hp.
Switch to assault if you get pulled or rooted. Whirling Pin towards your team. If WP gets avoided, detaunt an mdps, disarm another, and pray. I run CW3 for those ohshi moments.
Tactics: Masterful Aim, staple. Powerful Draw, staple, Leading shots in group (you can go Discerning Offense outside of group) because it's damn good: Increase the crits on your whole party (healing, melee, ranged), and Instinctive Aim I consider another staple but only because I trust my group and myself with backup and positioning. The toughness you lose hurts, but the WS and BS you gain is gigantic. This enables you to hit soft cap with BS easily (all my talis are in WS).
For renown abilities, I'm very defensive. Full dodge/disrupt tree, CW3, then currently I pick up random ranged crit or reduction to be crit. If you're leveling a SW, I would get CW2 at the least. That + the M1 can save you in a lot of situations.