Specifically I'm asking about Lair Assault: Kill the Wizard, but would also like to know if this is an overall rule for Lair Assaults. It's my first Lair Assault and I want to build my potential PCs as optimized as I possibly can within the confines of the Lair Assault rules. I know long and short rests are prohibited, but I am specifically trying to figure out if I should be picking encounter powers or dailies for utilities and also whether or not I should weigh encounter powers that have "until the end of the encounter" effects as being more optimized/powerful.
Typically, yes they are. No resting is allowed, and I believe that "until end of encounter" effects are sustained the entire time.
This provides an interesting form of action economy for these kinds of effects. You probably only want one daily stance power, unless you anticipate going unconcious and losing it.
Things that continue without your intervention are probably better than sustain minor effects as they will hurt your action economy the whole game.
Note that, unlike Encounters, "D&D Lair Assault allows players to utilize the entire breadth of the 4th Edition rules" (WotC website).