Which side usually wins in a battle between these two powerful creatures? Will fighting at night give the vampires a bigger chance at winning?
common werewolf vs common vampire
a group of vampires vs a group of werewolves
a very powerful werewolf vs a very powerful vampire

Vampires and werewolves in ES never really had ay problems with each other, save for two mentions in Daggerfall where a vampire had to kill a pack of Lycanthropes in order to take control of a location and a vampire mentioning how delicious werewolves taste. Other than that, vampires usually fight off each other while werewolves live in seclusion.

This kind of fight doesn't really happen in the lore. Werewolves are homicidal enough (since the disease compels them to assault people) that they might pick a fight with a vampire, but there is no special animosity between the two.

Anyway, the battle would pretty much have to occur at night, since under normal circumstances lycanthropes transform when a moon is full.

Common werewolf vs common vampire:
There is no such thing as a common vampire. Given all the different strains of Vampirism, a "common" vampire of one strain (say, the cyrodillic strain) may perform very differently compared to an Aundae or a Volkihar. A vampire with skills in magic or a silver weapon could very well kill a werewolf, if their prowess in either magic or the martial arts is sufficient.

Group vs. group.

Depends on the vampires strain and combat prowess.

very powerful vs. very powerful
depends on strain and combat prowess. Though a vampire with magic would be at an advantage.

It depends on how the curse would affect a werewolf.

A vampire can get stronger with age. Whereas a Werewolf may not. Are all werewolves massivly strong from the start? Or do they also get stronger in their werewolf form as they get older? Werewolves are never examined in great detail in TES, because they're always dead when examined.

Werewolves can get stronger if "blessed" by Hircine. It's conceivable that the longer a werewolf lives, the more abilities they get from Hircine for doing well (if they do well).

Beyond that, all we have is game mechanics. In Bloodmoon, your stats were changed to specific values regardless of their normal values, while in Daggerfall, they increased a set amount from their normal values.