Many people think that there aren't many distinct differences between those beverages but as it turns out it isn't completely true.
The caffeine content in cold brew coffee or Americano is nowhere near as different as it is when comparing the same drink with a different base (for example Coca Cola vs Pepsi).
But still, there are enough hints out there that point out to the fact that cold brewed coffee has at least 10% more caffeine than regular Americano because of its slower brewing process. To put it into numbers, an 8 oz cup of cold brew would contain 95 mg of caffeine while the same volume of drip coffee would have around 108mg / 14 oz.
However, these values should be taken with a grain of salt because there is a lot of variability when it comes to caffeine levels in coffee. The amount of caffeine present also depends on the origin of coffee beans, roast level, brewing method etc so in order to get more accurate number you would need to test several cups of coffee made using different methods.
Apart from the higher caffeine content, cold brew coffee is often seen as having a smoother taste and it's less acidic than Americano. This is because during the cold brewing process acids are less likely to develop which gives a more mellow taste to the beverage. Some people also find that cold brew coffee doesn't cause that jittery feeling that regular coffee can sometimes have.
On the other hand, Americano is a very versatile drink and it can be made using different types of coffee - from light to dark roasts. It's also a great way to enjoy espresso without having to go through the process of making an individual shot.
Truth be told, there is no clear cut answer when it comes to deciding which of these two drinks is better. Both cold brew coffee and Americano have their own unique set of benefits and downsides that you should take into account before making your final decision.
If you're looking for a strong caffeine buzz then go with cold brew coffee, but if you want something that has a more complex flavor profile then Americano might be a better choice for you!