Where'd the other thread go? Man it's been a while since I went on Smogon. Either way,
If you're willing to add even one more EV training hotspot for Atk, I proposed one more which works slightly better in White version (I think back when I proposed it Serebii had it labelled wrong).
Route 10
http://www.serebii.net/pokearth/unova/route10.shtml
The pros,
White Version:
Has 2 pokemon which give 2 Atk EV's (50%)
One that gives 1 Atk EV (30%)
Doubles Grass
Cons:
Two pokemon that give HP (20%)
So 80% of your battles get you attack EV's, and with doubles grass, you can probably get EV's far quicker than the other areas (since the doubles grass outside of dragonspiral isn't accessible). The downside is the random 20% HP, but since it's doubles grass, it's unlikely that you get nothing but HP, i.e. every battle is worth something. Just carry a smoke ball on the second pokemon or something and you can just run after you've killed what matters.
Pros,
Black:
3 Pokemon that give 2 Atk EV's (70%)
Doubles Grass
Cons:
1 Poke that gives 1 Def EV (30%)
Black ended up a little worse, but the fact that you've still got doubles grass means this area should be faster than dragonspiral tower etc..., especially with all 3 pokemon giving 2 Atk EV's. Just run from the Vullaby's and you'll be good, same smoke ball principle.
OVERALL:
The fact that at least 70% of the pokemon in both versions give Atk EV's (At least 50% give 2!) and the presence of doubles grass (2x quicker battling) means that EV training will go a lot faster here than any of the current proposed areas (that are accessible year-round). Watch out for undesired EV's and you're fine.
"I've found the Doubles Grass in Route 1 to be reliable for ATK EVs. You get Scraggy (+1 ATK), and Watchog and Herdier (+2 ATK). Minor problem in surfing across a Basculin pool to get there, but you get them quite quickly."
Though that's even better, haha. Though yes, a bit farther out of the way.