If you haven't read my post, I am new to the Red Sea (but have done lots of research and reading), and just booked a spot on the Tillis in June for a Deep South Safari in June.
I am not sure I agree with the only "3-4 companies". Liveaboards are like restaurants, bad ones go out of business fast. You will probably be okay with anyone with a few years of good reviews.
I also strongly considered Blue-O-Two and Red Sea Explorers. Price and timing played a large role, but I like the idea of a locally owned and operated company.
I really wanted to see Brothers, and will someday, but don't have 50 dives.
If you want wrecks, North is the way to go.
If you care about colorful corals and small fish, people are surprisingly split, with several saying South is better than North and others saying the opposite. North might be better for colorful soft coral and South for hard coral.
Supposedly South is better for sharks, dolphins and larger fish.
I've watched hours of Youtube, which has some great videos of Red Sea dive sites. However I am skeptical, as a bad video of a great dive (I've taken several) can make a great site look bad. And while it is harder to do, a really great video of a mediocre site can make it look great.
From people I've talked to in person who went to the Red Sea, all the diving was amazing, with great visibility and interesting sea life.