Playing a storm giant vs human, elf, and two wood elf hunters, I'd go with the latter.

I tanked better with the smaller, more dextrous races. I don't know that the archery defense is skill or skill + dex based, but dodge is dex based and with a bow you cannot parry.

I can't speak to hitting with aimed shot; hunters were tweaked between my first hunter (storm giant) and my three subsequent hunters.

There is no difference in damage based upon size, but higher damroll (and strength boosts damroll) increased archery damage.

The duration of observe (and consequently the number of observations you can acquire) seems to be based on your intelligence, and maybe a comparison of your intelligence to your foe. I determined this by switching out int gear as I stalked someone. With only one or two stalks, I perceived no benefit.