When playing terran and you make your first baracks you have three options
1) make a marine
2) make a tech lab
3) make a reactor

what are the advantages and disadvantages between the options?

marine, kill scout

this

Marine protects against any early aggression, kills worker if it made it into the base before your wall.
Reactor allows you to produce 2 marines or 2 helions, both of which are pointless since you delay your initial marine and 1 marine can hold off ANYTHING at the time it comes out if you're walled and helions simply won't be ready in time to be built if you reactor first since you won't have gas for a factory nor will it build in time.
Tech lab can be useful for specific things, but a marine first almost always trumps it.

The fourth option you've neglected is simply skip marine, skip addon, expo, which is useful against a variety of openings.

Pretty much always making a marine right away.

Unless your build is specific to the point where it's more beneficial to not make the marine I guess.

Make at least 1 marine before doing any add ons so you can deny scouts.

Disadvantages with 2 and 3 including any non-retard will addonblock you into game over

This post was edited by Svartermetalisk on Dec 24 2012 03:55am

try maxing an army with only 3 rax for 15 mins, shit is op