1. WOw!! THats hard because what alot of people don't realize is that your olfactory part of the brain is actually linked to your ability to taste. That is why when you have a cold and a blocked nose, you can't taste your food. If you didn't have one, the other would also be greatly diminished so it almost doesn't make a difference to pick one over the other.

2. Life would definitely be difficult without hearing but even harder without being able to see so if I had to pick one I can do without it would be hearing. Alhamdullialah that I have both!!!!!

probably eye sight is more important than smell, but I hear blind men have incredable sense of touch ... which is as important as the above mentioned senses ...

smell? no way, I love the scent of a woman ... ask Al Pacino :)