Zabuza wins high difficulty.
Some people just look at the number of people and say this team wins without actually understanding how the battle will play out.
Numbers don't mean much against silent killing as shown in the War Arc where it took a bunch of team work and a complicated plan from Kakashi to stop Zabuza. If it wasn't for Kakashi and his plan, who knows how many people Zabuza would have killed. Considering a young Zabuza that had not even joined the academy was able to kill 100 genins, a mature Zabuza can take out two low jounin levels and one mid jounin level ninja. Zabuza himself is a high jounin level shinobi so it shouldn't be impossible for him to do so just because he is outnumbered.
Anyway, Asuma alone can push Zabuza to mid difficulty which is why this is a high difficulty fight for Zabuza. Without Asuma, Zabuza would win with low difficulty.
The fight would probably being with Zabuza blinding the opposition with hidden mist, creating several water clones and then sending them to fight the jounins. Meanwhile, Asuma would bring out his chakra blades, Shizune would bring out her poisonous needles and Anko would probably bring out her snakes located inside her arm pits. In order to defend against silent killing, the jounin would have to form a Manji formation to avoid being caught off guard from behind, nevertheless, if they do use this formation, Zabuza can blast them with a water dragon so using this formation to counter silent killing will yield no tangible results.
If the team decides to split up, Zabuza can easily manage to get behind them and finish them off relatively easily.
As for team 1's potential counters to the hidden mist and silent killing. These could include Asuma's burning ash to evaporate the mist's water molecules or Asuma's wind dust cloud to blow the mist away. The burning ash is a flawed counter because it produces a lot of blinding smoke which will conceal Zabuza and it is a linear attack that won't clear out the mist from the sides and back, which is Zabuza's preferred and most effective method of silent killing. Similarly, the wind dust cloud is also a flawed counter for similar reasons. It can create a dust cloud and will only create a gaping hole in the mist in front of the user. Again the sides and behind of a person are still exposed.
Anko's snakes may have heat sensing abilities, but her team mates can throw off that sensory ability because her team mates are also the same temperature as Zabuza. Moreover, water clones are made out of water so those heat sensory abilities won't differentiate them from the environment. Shizune's poison cloud will only serve to poison her own team mates as Zabuza is cautious enough to utilize water clones.
Anyway Zabuza's superiority is clearly evident.