Which grease is for what? I used to think as simple as lubcirants and grease, now that I'm off to buy grease to assemble a bike I'm confronted with dozens of different types of greases.

Does it matter what grease I buy? If absolutely not what grease do I use for what?
The only question I would have is if the bike is Carbon Fiber or not. I'm guessing it's not and is an alloy (metal) bike. Just like cars, there are tons of stuff people will try to sell with magical properties. Ignore them. 

There are two greases I use: The first is because it is everywhere, cheap and easy to apply thanks to the tube:



If you want more grease for your money, you can't beat Lucas Marine Grease:



In the end either will do the job very well. The marine grease is longer lasting and theoretically more rust resistant. But I use it because it does the job well, a tube lasts forever (use a plastic spoon to dig some out when needed) and it's thicker than Park's stuff.

I carry the Park stuff with me on a mobile job because it is easy to apply and customers like names they recognize.  The cost is the same for either. I'd vote for Park due to convenience.