The first thing is that they really have two completely different cultures that appeal to completely different people. The way I describe it is that the consulting companies are basically an extension of Business School, while FAANG is an extension of Engineering School. The culture at a consultancy is generally a lot more social, with huge, alcohol-filled parties being the norm (if you think FAANG parties are big, B4 parties are twice as big and happen 10x as often). They also put a lot more emphasis on "group work" where the main way of getting tasks done is to get together in a room and work side-by-side while having continuous review and conversation.
If you're a person that likes to often go out to bars, have fancy team dinners at chic restaurants, work in groups, and spend a lot of time building relationships with your coworkers, you probably would like B4. What I just described might sound absolutely horrible to many HNers, but there are many people that really dig that lifestyle.
On the other hand, if you are a stereotypical computer engineer that would rather go home and recharge rather than go to a bar, maybe have a nice company-provided dinner every now and then but not every night, do your best work heads-down without any interruption or talking, and think "work is for work, not for making friends", then you certainly wouldn't like B4 and would probably like FAANG.
As for pay, B4 starts out a bit lower than FAANG but salary at consultancies grows much, much faster. Getting a promotion every 2-3 years is expected, with large salary bumps and large bonuses even in non-promo years. When I left B4 to FAANG, my pay almost doubled, but due to the way B4 pay scales, if I went back to B4 now I would likely make more at B4.
Career progression is also very different at B4 vs FAANG. There is no "Individual Contributor vs Management" track at B4. Everyone starts as an IC, and then slowly starts taking on more management responsibilities. For me personally, I really prefer this because it means I get to be a manager that makes strategic decisions and mentor a team, but also still do "hands on" work as much as I want. FAANG, on the other hand, I have to make a decision whether I want to be an IC (where I will only have some mentorship/manager responsibilities, if any) or Manager (where I will be doing considerably less hands-on work, if any).
And last, tech consulting at the big consultancies can genuinely be fun. You get to hop around to new clients/projects every couple months, working on and learning new types of work. If you do find a type of work you really like, you can specialize in it and stick with it as you please. For some people, switching clients and meeting new teams to work with, being "the expert" in the room, and always running into new problems is fun.