Fizz is a champion where you can max any of the 3 abilities first and you would still do everything right. However In high elo play very small things must be respected.
Now let's take a look at his ability scalings and cooldowns:
Physical Damage: 100% AD
Magic Damage: 10 / 40 / 70 / 100 / 130 (+ 60% AP)
Cost: 50 / 55 / 60 / 65 / 70 Mana
Cooldown: 10 / 9 / 8 / 7 / 6
Passive Magic Damage: 30 / 40 / 50 / 60 / 70 (+ 35% AP) (+ 4 / 5 / 6 / 7 / 8% of target's missing health)
On-Hit Magic Damage: 10 / 15 / 20 / 25 / 30 (+ 25% AP)
Cost: 40 Mana
Magic Damage: 70 / 120 / 170 / 220 / 270 (+ 75% AP)
Slow: 40 / 45 / 50 / 55 / 60%
Cost: 90 / 100 / 110 / 120 / 130 Mana
Cooldown: 16 / 14 / 12 / 10 / 8
So what does actually speak for Maxing E > Q`?
- You have 50 Damage per level instead of 30
- Harder Slow which is your only CC Pre-6
- Cooldown gets lowered per-level while being an Invulnerability spell
- Better AoE damage
- Really High Mana cost
- Harder to hit
Now here's the thing why especially higher elo players tend to max E instead of Q: They don't screw up their spells as often as Low Elo players do. When I'm playing on smurfs one thing that I see really often is that lower elo players just use their spells randomly. Someone who plays in higher elo uses his spells when he needs to and when he's certain that he will hit. These two things will compensate the negative aspects of maxing E.
Now When should you max what?
Max Q if...
- You are unexperienced with Fizz and you want to have a 100% hit dmg spell
- You are playing AD Fizz
- You are not experienced with mana-management
Max W if...
- You are playing Jungle Fizz
Max E if...
- You are Certain that you will hit with it
- You need wave clear
- You get ganked a lot
- You need CC
As you can see there are a lot aspects that speak pro maxing E. You can of course max W or Q in any situation aswell without screwing up too hard but E is just a lot better if you master its utilty.