Okay, this thread has gotten WAY off topic.
Guys, we are comparing careful shot and twin strike in this thread. We are not going through every fighter power in the game. Do that in another thread.
Back to the topic on hand. People are asking a logical question, is it that careful shot is too weak, or is twin shot too good? For that answer, let's turn to other classes and see what they have.
The rogue is the most comparable, both are strikers that use weapons. The rogue's piercing shot is a weapon attack vs reflex. The difference between Reflex and AC varies widely among the monsters. Some have as high as a +6 or so difference. But I think the vast majority have at least a +2 difference. And the rogue gets to keep his dex bonus to damage.
Then there's the paladin's valiant strike, which is another "sure hitting" ability. The paladin gets at least a +1 to attack, and will often have a +2. Further, he could have as high as +6 or even +8. And once again the paladin gets to keep his str bonus to damage.
Comparing those models, changing the ranger's careful shot to +2 to attack, regular damage seems completely reasonable. And it also makes sense from a flavor perspective. The ranger gets to add his dex bonus with a ranged weapon because of his accuracy. A "careful" shot should be highly accurate (ie dex is added to damage). While a twin shot, where you are literally firing two arrows as fast as you can, would not have that accuracy and so no dex mod.
I ran the numbers with this assumption in mind, and its almost there. If we assume a +4 dex and no hunter's quarry, careful shot is always averaging more damage than twin strike, but only about .3 more. However, twin strike's accuracy is higher. You are more consistently hitting with twin strike, and you have the option is hitting two targets, making it a much better mook killer. However, when you add in hunter's quarry, twin strike takes over again.
So one more tweak to careful shot. We now add +3 to the attack roll. With that in mind, careful shot takes back the damage crown, average about .5 damage more than twin shot. Twin shot still carries the advantages of higher accuracy and mook killing, and I think both are now fairly competitive with each other.
With that in mind, I think changing careful shot to attack +3, damage 1[w] + dex should solve the problem.