It mostly depends on your demon level and the level of the survivors. Without going too deep in to it, 5 players with little game knowledge heavily favors demon. 5 players with high knowledge heavily favors survivors.

General tip: Trap chests at the start of the game, they give the most exp by far. Ignore the trees early on.

Without levels, all the demons struggle because their units get staggered or just instant killed easily.

Necromancer is probably the easiest demon to start with for several reasons. The most important one is it gets the rocksteady(balance bar) skills super early on which helps your units actually have a chance to fight back. This lets them do damage and helps you level up. The demons that have rocksteady later struggle hard.