Based on the Consumer Report review, Altima is the top among the three.
Accord(LX) is the 2nd, then Camry.
Car and Driver also reviewed 7 mainstream sedans in March issue. Accord EX is the top, the 2nd is Altima, then Camry(it's actually 08 model and it's 5th after Malibu and Sonata).
Accord EX would be $2K more expensive than Altima and Camry. If considering the same price range(Accord LX model), Altima is still the
best among the 3. This is inline with what Consumer Report rated.
In terms of the style, I think Altima is the best. Especially, the new 2.5S
with two mufflers on each side looks really sporty. Its acceleration and brake distance also are the best among the 3. Its handling just slightly behind Accord-EX.
The things that I worry about Altima are its CVT transmission(never have experience) and its long term durability and realibility(compare to Camry and Accord). Consumer Report also show the average problems of 10 years,
from least(best) to most problems after 10 years. Among the 3 the order is Toyota, Honda and Nissan. I guess that's one of the main reasons that Toyota still has the best re-sell value, and Nissan has the worst among the 3.
This is really 鱼与熊掌不能兼得.