Play what you like....period.
Shaman's are the most challenging class to play. If your looking for "OMG I so PWND JU" in dmg, you might think about taking something else to endgame. Its not that Sham's can't put up impressive #'s (in dmg or healing)...it just takes A LOT more work to do so, and a much more concious lvl of game play, compared to other classes.
The WF nerf is something to complain about, granted its not the only thing to complain about! WF nerf affects the ppl that just wanted the WTF dmg. For thoughs that solely played sham for JUST that....then ya, its a bad nerf, from that perspective. Sham's can't do the "rampage" type kill streaks in BG's like they used too...or at least not as easy anyhow. If you don't mind just being in the 5 top of the dmg totals, AND the healing totals, then Sham might still have interests to you all the way to 70. I don't know of what "horror" stories you've ever heard of regarding sham dmg output. If anything Sham's can be SHOCKING dmg dealers..but at a cost! Sham's can do SOO much dmg in such a short span of time...yet have absolutely no way to mitigate the hate, and mail armor doesn't completely make us MP friendly to devoted healers.
Its not that Sham's don't make great dps, but in order for a good sham to completely unload on a target in PvE, there needs to be "steller" hate management. Then of course, comes the other problem even if this fact is meet. MP Pool. Sham's have the lowest in the game...bar none! A few SS or shocks, a couple of heals here and there, and before you know it...your /oom. Enh by far has the best dmg vs. MP consumption of any of the specs, but its far from safe from this problem.
I wouldn't say Resto is the most "viable", but it is the most "wanted". Course, when hasn't that ever been a factor :p Its simple game dynamics, out of the 9 classes in the game, and of the 3 specs each class has....that basically means that there's 23 dps setups in the game!!! And only 4 healing setups. Its no wonder any "healer" is a wanted!!
Does is mean thats its the only "Viable" one? Not at all. But obviously its much easier to fill a dps slot, instead of a healer slot, when it comes to building pts. Sham's can bring TONS of dps to any pt, just lack other "toys" that any other dps can bring to a pt, thus sham dps is "replacable" by 21 other class/specs...from a dps perspective anyhow.
A Sham's nitch is still the fact that we can do alittle bit of everything, regarless of spec. One of the downsides to Resto is the fact that, in order to make the spec work for what its required to do, means you have to go DEEP into the spec, devoting at "least" 41 points to make it viable, from a endgame healer perspective anyhow. Other specs can support main healing in lower lvl outland instances, but sham's lack the staying power that other healing classes have...something thats required in many of the lv 70 instances, if they aren't geared & spec'd for it.
As irony would have it, the "hybrid" class, becomes very one dimentional, and lacks any significant contribution to dps. Kinda like a better armor'd holy priest, with less efficient heals. U'll be wanted by pugs and guild runs anywhere. Course, sham's are still "asked" to heal regardless of spec, and ppl still think we can fit into any situation a priest was in....and we won't in most cases.
In the end, its still up to you for spec and class. If you enjoy soloing and like a mix of doing everything...then ya any spec of sham is for you. If you are more raid/pt focused, and consistantly play with groups of friends...and LIKE healing...then ya Resto might be more you. Course, your Priest "should" always be a better healer than any shaman...so if your more focused on doing that for ppl endgame....then don't pick sham.