Depends on what you want for damage output, frequency of damage, and power spikes.
1- Damage output
This is the amount of damage that an ADC can put out. Due to their nature as a marksman, all of them will put out tons of damage late game- the damage output based on power spikes/timing is different, however. Examples: All ADC's will put out massive damage late game, but people like Caitlin and Draven will put out a lot of damage when they first come to lane with their auto's, and Graves or Lucian (The same champion) will put out a lot with their abilities at level 1. Contrary to this, Vayne and Twitch will put out a lot when they get a BotRK due to the synergy it has with their kits. Kog'Maw and Corki get big spikes when they get a triforce. Others, like Sivir and Miss Fortune, will simply scale up through the game- they don't hit GIANT spikes, they just ramp up over the game.
2- Frequency of Damage
This can also be called the speed of output- how fast a champion deals their damage. This is what says a champion is dealing damage with- Graves' all-in vs. Caitlin's constant poke. Graves' all-in will deal a lot of damage, but he can't do the whole thing constantly. He'll go in for a burst of damage, and then walk away if he can't secure the kill. Opposing this, Cait will throw out Q's and auto's constantly, laying down poke consistently. It's significantly higher frequency of damage, but much smaller damage output with each shot.
Cait- High frequency, low speed of output. Graves- Low frequency, high speed of output.
The difference in playstyle is significant. Cait will keep you at bay from small threat of auto's and Q's due to her range (Similar with Sivir and MF), but has relatively low kill pressure due to the low chance of surprise amounts of high damage. Opposed to this, Graves (As well as Lucian, Tristana, pre-6 Corki) will have much higher kill pressure when you're lower as they can pop a high burst of damage, taking someone from mid-health to dead in a short time. However, this comes with a much higher mana expenditure- and thus lower sustain. The nature of their bursty play means that they don't get much back from lifesteal.
3- Power spikes
These can be localized to either items, abilities, or there might be multiples when they get a few smaller power spikes. People like Draven will get big spikes with each of his big ticket AD items, as he multiplies each AD bonus- very snowbally due to his passive. Other than this, Koggles and Corki will both hit a single pretty big spike once they hit triforce, but Kog'Maw will hit another one with a BotRK due to synergy gains.
Now if you want to categorize this, you can use a format like:
Champion: Power(early):Power(midgame):Power(lategame) (All of which are in relation to other ADC's), Burst (1-10, 1 is all sustained damage, 10 is all burst damage- relates closely to aa damage vs skill damage. closer to 1 also tends to imply higher hp/mana sustain as well)
So just a couple:
Graves: 5:9:7, 9
Corki: 4:10:6, 6-4 (Pre-6, post-6 due to ult+triforce)
Caitlin: 8:7:5, 2
Kog'Maw: 2:6:10, 4
Varus: 5:7:8, 2
? Or should I go for a more skill based champion, that focuses more on mechanics like 
? What's the pros and cons of that?
can ruin AA heavy champs, but then the Skill focused ADCs usually don't have lasting mana pools either.
