Since the Navy mainly determines power through bounty. They seem strong but Whitebeard was able to fight all three admirals at one. Also the Commanders of Whitebeard were on par with the Admirals. So how strong are the Admirals? How much bounty would they get if they got one?
The Navy actually doesn't determine bounty based entirely on power, they also base it on how badly they want the particular guy caught.
Considering how DonFlamingo's bounty was 340 million beli, and he was a pretty big deal, It appears that the marines start leveling out the bounties around the 300-400 million range.
That taken into account, If the admirals were pirates, their bounties would likely be in the 300 million range.
As far as power goes (and power is not that quantifiable in one piece), they're all in the top league, and so far, the only character who was formally introduced who can be said to have a very clear advantage over the admirals is Whitebeard, and he's dead.
the Other Yonko are very likely to be stronger than any particular admiral, but that's not necessarily a concrete rule, and we yet to have a good measure of their power.
All of the Admirals are likely 1 step below the Four Emperors. I think it would be realistic to say that if Akainu was a pirate, he´d probably be around the 500-700 million range.
Aokiji is the least hostile and probably the weakest too, though it´s hard to say how they compare against each other.
Akainu is the most hostile and potentially the strongest of them. Lava is one of the most ridiculous powers imaginable, being both heavy enough to choke out fire and gas/air and still liquid, oh and it´s at least 1000 degrees Celsius as well.
What I want to say though is that I think Kizaru is the strongest of the Admirals. Think about this for a moment. You can counter ice with fire and other heat-related things or things that can´t be frozen. How the hell do you counter light? Light moves at 300 thousand kilometers a second (and therefore hits with that force too, making Kizaru potentially the physically strongest character in the One Piece world), is intangible, can bounce off of things, can cut and pierce things in the form of a laser. That´s probably the most overpowered possibly Devil Fruit power.
To put it shortly, while they aren´t the most powerful characters in the series, the Straw Hats probably still don´t stand a chance against one and they are pretty close to the top.
You know how in some stories there are some characters who are like, god-like overpowered? Thats how the admirals are. When luffy was fighting aokiji, the latter was barely using his full power and easily owned him. Its difficult to hit them since they can turn into their own element (except by using sea stone or haki), but the element akainu turns into probably makes him more dangerous. If you touch ice, part of you will freeze. Light, nothing will happen. Magma? your body will evaporate and die. I'd say Aokiji's powers are more accurate, Akainu's are more destructive, while Kizaru is a combination of both, but I think he kinda balances. I'd say currently in one piece they're all equal. Sure, it did take 10 days for Akainu to beat Aokiji, but with that much time they barely seemed to have been outmatched.