Do you know why everyone keeps saying the same thing? Because there is no way the Sannin can beat any of those things.
(Sasuke's) Tsukuyomi - Can at least catch them in it for a little while. Just enough to throw them off.
(Sasuke's) Susanoo - Danzo had to use a summon and an A rank wind jutsu to make a hole in an incomplete Susanoo. Afterwards he got the completed version against Kakashi but he went blind. So an almost absolute defense with very fast arrows. Fast enough so Kakashi couldn't dodge.
(Itachi's) Susanoo - unbeatable as long as it is up. He has the ultimate defense with the Yata mirror and the Totsuka sword. All of the summoning would easily be sealed with Itachi's Susanoo. aPlus you can't hurt him while in there.
(Itachi's) Tsukuyomi - Unbeatable, no one can break out of it except for Sasuke or possibly Madara, immense trauma to the brain and body. It only lasts one second so how are they going to defend against this? Look at his feet the whole time? That leads to my next point.
(Both) Amaterasu - Only Oro has a defense against this as he can regenerate any body part if he cuts off the burning part. If Jiraiya or Tsunade is hit they are done for or they can cut off their limbs, without which they would lose easily. And if they don't look at Itachi's or Sasuke's eyes then they can't see if Amaterasu is coming can they? NO
Itachi's regular genjutsu - Strong enough to beat Oro, and Deidara, and Sasuke with. How can they break out of a genjutsu if they don't know that they are in it? Answer me that. And don't say oh the others can break them out because guess what? They would either be in a genjutsu or not know that their teammate was in one. What are they going to do, hold hands to check their chakras?
Fire jutsu - The Uchiha are fire masters and only Jiraiya uses fire as well, Oro uses wind which guess what? Is weak to fire. Tsunade has not shown any elements yet I think.
Speed - Both Itachi and Sasuke are normally faster than any of the Sannin, Itachi is way way faster than them. Plus they have the sharingan which helps a ton in taijutsu. If you don't believe me look up the normal sharingan abilities.
Sharingan bonuses - ability to copy and memorize jutsu, and see chakra, and track movement, and predict where the opponent will be.
Chakra - Sasuke has alot, Itachi apparently had more than Sasuke did even with his Curse Mark and Itachi was sick. So no BS about Itachi having low chakra.
Intelligence - Itachi is easily the smartest of the five with Jiraiya and Oro probably coming in second and third. In battle I would think Sasuke is smarter than Tsunade.
Summonings - Slug, Snake, Toad, Hawk. However the summonings don't really factor in as they could be beaten easily with Susanoo. No way are any of the toads or Katsuya faster than Kakashi and he couldn't dodge that Susanoo arrow and Itachi has the Totsuka sword which is an automatic seal if it pierces you at all. One slash and you are toast.
Make valid counterarguments please. DO IT. How would the Sannin win? They can't beat
Tsukuyomi: would be very difficult to pull of against the sannin as they will not just blindly fall into a genjutsu, it can also be countered using eachother or summons like ma and pa the same as B used the monster inside him
(Sasuke's) Susanoo: Both Jiraiya and Orochimaru got extremely power full firepower if Danzo can do it these 2 sure can
(Itachi's) Susanoo: that it hasnt been broken doesnt mean its unbeatable and it Put a huge straign on Itatchi whos main weakness is stamina
(Itachi's) Tsukuyomi: same as sasukes
(Both) Amaterasu: I already went over the defense against it in a post above.
Itachi's regular genjutsu: even easier to counter then Tsukuyomi
Fire style jutsu: No effect on stomach of the fire toad, orochimaru has been seen using different elements then wind and Tsunade has an element wich has not been seen before also they have their summons who utilize their own elements
Speed - they dont look up their stats and you will see that their speed is not higher then then Jiraiya and Orochimaru
Sharingan bonuses - Basic sharingan gives them an edge but its not a counter to All of the sannisn ninjutsu wich they have plenty and its sure not the greatest weapon against a highly skilled ninja who wont be fooled by it
Chakra - Its always been stated that Itachis weakness is his stamina and chakra reserves and using his powerfull jutsu is very straining for him
Intelligence - Why is Itatchi easly the smartest Jiraiya is on par with him and we havent seen mush of tsunade yet. Also being smart doesnt cut it the sannin got way more knowledge so they have the uperhand in intelligence
Summonings - Both manda and katsuyu have been shown to be able to take a lot of damage, also katsuyu can be attatched to the sannin to heal them and u cont forget the whole army of toads wich wield powerfull jutsu themselfs. And on top of that u got MA and PA who posses a genjutsu that cant be seen by the sharingan. Even if they could defeat the summonings while fighting the sannin all at once it would leave them with no chakra.