Oh, I see -- 4e took all the problem mechanics like knockdown, stun, etc. and made sure at-will powers couldn't do any of those. It's okay if encounter or daily powers do those, because they're a limited resource. But in a 3e-like system with tactical maneuvers, you pretty much need to have an at-will knockdown attack, and that's difficult to balance.
Actually, there are 4e at will powers with knockdown, but the damage is incredibly low relative to other at will powers. For example, our level 2 fighter in the current game I'm running has the following at will attack options:
+8 v ac, 1d12+5, reroll 1s and 2s on damage
+10 v ac, 1d12+8, reroll 1s and 2s, but grant combat advantage
+8 v fortitude, 4 damage, knock the target prone
If you're really sharp, you can use the knock prone attack to deny your enemy an attack about every other round. Knock him prone, shift back a space. He stands, but cannot charge a target only one space away... so he loses an attack. On your next turn you'll have to fight him fairly, because if you shift in and hit him he'll just stand up and hit you back, and if you don't attack he'll just walk over and hit you. But then you can repeat the process.
That's not really what I meant. In 5e, the fighter will probably not get daily or encounter powers.
What I meant was, is there often a situation where one of a character's at-will powers is so good that he never uses the other one? I always played casters in 4e, and there was a big difference between Magic Missile and Scorching Burst, but what about for the fighty types?
The reason I ask is that the design team is likely to balance the game using 4e technology, so if it worked in 4e, it'll probably be fine in 5e.
The answer is... sort of? You don't notice it much because of all the aforementioned encounter and daily powers. Lets say that one of your at will powers is really situational, and the other is usually better. If a fight lasts 8 rounds, you'll still probably only go for the better at will power maybe... three times?
The other key is that most at will powers are balanced by being situational. So if you have one go-to power that you use when you just want to hurt something, you don't feel like its overpowered compared to your situational one so long as the situation comes up every so often. My own fighter, from back in the day, had three at will attacks (human, old rules):
Hit the enemy, deal regular damage, shift one, draw the enemy into your previous space
Hit the enemy, deal regular damage, deal light damage to another adjacent enemy
Hit the enemy, deal regular damage, gain temporary hit points.
The third might slightly overshadow the other, but the others are valuable in their own way. If a fight was poorly set up, I might end up spamming the last one until the bad guy's hit points went away. I'm un-fondly remembering a regenerating werewolf here that took twenty minutes of just battering away at it until it collapsed. I'm sure I spammed the last one above like mad. But that was an unusual situation.
There are certainly classes that do spam the same at will. But here's my experience of classes in play:
Ranger- spams twin strike because its AMAZING, but has chosen a very situational secondary at will. This makes sense, if your favorite does incredible damage, you pick a weird, situational back up that won't overlap with the first.
Cleric- spams an attack that gives temp hp, because its disproportionately good compared to her other at will options.
Wizard- does not spam. Both choices have too much utility for that.
Paladin- does not spam.
Fighter- does not spam.
Rogue- a little but not a lot. One at will is better for damage, but the other is for repositioning. He needs combat advantage, so he uses the latter a lot against enemies who his team can't pin into one place.
Avenger- does spam, because at wills are the weak point in the Avenger design.
Druid- does not spam. The druid rewards shifting forms frequently, so she literally doesn't have the same at wills round by round.
Shaman- does spam, but has so much else going on that you'd never notice. INCREDIBLY complex class to play.
Invoker- a little spam. Has a multi-target spell, and a single target spell. Spams whichever is appropriate. Technically uses a good mix, but the at wills are a little flavorless so it feels more spammy than it really is.
Psion- feels more spammy than it really is because the psionics core mechanic involves "augmenting" your at will powers. So your encounter powers don't feel quite as different as you might like.
The others I don't have enough experience with to really comment. And mind you, this is using a 4e conception of spam- by 3e standards where your fightery types have one core attack they've carefully cultivated and now use every round, none of these classes spams.