1_ I usually prefer "let's build"s. I have seen so many speedbuilds that I find them boring now. But I recently watched Plumbella's Let's Build series. It was so much more original and inspired me to play after every episode!
2_ I really dislike when the storyline is too basic or when something very unoriginal happens. For example teen pregnancies. I usually stop watching the LP when that kind of thing happens.
Skillbuilding is also very boring imo.
3_ If the quality of the sound is very bad, if the youtuber talks too much at the beginning (three minutes of saying «hey! I'm doing a new LP!» before presenting the characters and situation, like... we know!).
I'm not gonna lie, I also really don't like alpha cc so I don't watch the LPs with that sort of custom content.
I don't watch runaway teen or homeless challenges anymore unless there is a very good new idea for it (the backstory or an original way for the person to earn money).
Also, english is not my first language so if the person doesn't enunciate clearly, it's annoying. It's nice to have subtitles but not always necessary (I understand Plumbella and Deligracy though they have non american accents).
4_ Both!
5_ I don't mind either way. The most important is that you are comfortable because if you're not, we can feel it and it reduces the quality of your content. Just try both and decide what you like best!
I hope this helps and I wish you the best!
