What is the most dynamic and reliable defense vs. 1.e4 in your opinion?

In my opinion:

1. Sicilian

2. French

3. e4 e5

4. Caro-Kahn

The rest such as Pirc, Scandinavian and so on I call unreliable.

1. Sicilian

I don't think the Alekhine, Scandinavian, Pirc, Modern, etc are any less reliable than the Sicilian, French, Caro-Kann, 1...e5, etc. I think it really depends on what type of dynamic you want in your position and how much work ( and what type of work) you want to do. among other things!

For me, the Czech Defense:)

The Sicilian has a lot of theory and different lines, which makes almost no one able to prepare for every single one. Therefore, it can be manifested into an everlasting opening. Although you'd have to memorise a lot of theory. I once played the Sicilian but stopped a few years ago. The theory load was too much and I couldn't be bothered to memorise.

The Spanish / Ruy is just as bad (maybe worse?) about having enormous theory and tons of different lines.

I had to look this up, I didn't realize this move order had a name!

I didn't realize it either when I started playing it years ago. I always thought I was playing the Pirc

Caro-Kann

in my perspective opinion,it is the same move e4