Basically what I've been sayin.

each element has its unique advantages and disadvantages...but if you're speaking offense or defense the most offensive element is Fire and the most defensive is Air...Earth and Water are kinda on the fence with Earth leaning more toward offense and water leaning towards defense...

I think air and fire are tied as the strongest, then again the firebenders wiped every airbender out except our young avatar aang.

The 'strongest' bending element is definately earth. But the best in a fight is probably air, unless you are a blue firebender or you can use the lightning technique.
And the firebenders wiped the Airbenders out because they outnumbered them, took them by surprise AND took them down temple by temple.

My humble opinion:

Fire: Firebenders biggest advantage is, it can be created everywhere.
Firebenders biggest disadvantage is, it has no real defense nor the strength to break another benders defense. in principle a fire attack can't penetrate a strong earth defense nor can it get through a good en well made water defense.

Air:
Airbenders biggest advantage is the same as that of the firebenders.
Airbenders biggest disadvantage is again the same as that of the firebenders, it has no penetrating force.

Earth:
Earthbenders biggest advantage is that it has a strong defense against most other nation attacks. Example: air/fire attacks are completely useless against a stone wall (in principle ofcourse) and ice/water attacks are being absorbed by the same stone wall.
Earthbenders biggest disadvantage is that when there is no earth earthbenders can't do anything, like for instance on open sea.

Water:
Waterbenders biggest advantage is somewhat the same as that of the earthbenders, though in my opinion just a tad weaker.
Waterbenders biggest disadvantage is the same as that of the earthbenders though they have the option of taking water with them in a waterbag.

these are what i think i know about the elements in the avatar world.

i dont think any element has a distinct advantage over another, except in the cases where there is no water or earth to bend.?? i believe that the strength of a bender plays a signifigant role as well.?? for defensive and evasive??purposes air is strongest, while fire is almost purely an offensive force; earth and water are somewhat of a midway point between offence and defence.?? another thing you need to take into consideration is the surroundings, IE water benders are stronger in the??moonlight and fire benders are stronger during the day.?? this of course raises another question: do air and earth have certain times or events that make their bending stronger/weaker??? Overall i would have to say that the strongest element is the Avatar.?? Period.?? I mean thing about the strongest benders for each element that we have met, the Deserter/Iroh,????Master Paku,??Boomie, and Aang(?)(not really a fair choice since he is the avatar so we'll leave him out).?? but of all the others, i think it would be a very close fight, however you weigh it.?? (also note that in many cases, bending proficiency tends to show a close relationship with age and wisdom; although younger benders sometimes seem to exhibit greater amounts of raw power...)

look at all of the storms like tornado's which come from air also Aang has been able to take out quite a few firebenders at once, so I'm going to say air, because aang has shown great advanges useing air against the other elements.

the only reason the fire nation was able to take them out so easly is because they had the power of the comet, and I haven't seen them cath Aang yet so.

It's about the bender, and how they use their advantages and cover up their disadvantages.
The good thing about a water bender, is that it's faster than Earth, and if there isn't any around, it's still portable.
Air, is good because it's fast and can pierce some shields if used well. And it can be made anywhere.
Earth is good because it's strong defense, and it's strength.
If a giant boulder was dropped on me from 100 feet high or so, I'm pretty sure I'd die.
Water is good because it can be a solid, or a liquid, and is probably the best at piercing things. Aang didn't chip the metal with Air, did he?
Earth and Water are good against themselves because they can simply reverse the attack.
Fire is good because it is fast, strong and induces long term pain. If I got an Air cut, or water splashed, it wouldn't hurt forever.

I'm just gonna say fire and heres why, they're the only bending that can become superpowerful from an otherworldly source, at least that we know of. I think this is highly strange and also, incredibly unfair. For all the balance the creators put into the show it seems like they gave the firebenders some kind of huge advantage here. Other than that though it all depends on what you mean by strength

i think the most powerful benders are the fire benders cause unlike water and earth they dont need the actual land or water around them they just shoot it out of wherever, and the airbenders, wel, fire is fueled from oxygen so an airbending attack should jus make the firebending attack just stronger. shouldnt it?