Tinker Builds

Not always.

ALways go Laser /Rocket first. Then get March

Basically, what Sando said: competitive players usually go for the March of the Machines build as it makes ancient farming super easy and you want those Boots of Travel as soon as possible; pub players tend to stick to the ganking build (Laser - Rocket) because they either prefer ganking and don't mind having a late pair of BoT or because farming ancients requires good timing for stacking and controlling your own lane at the same time, and they prefer roaming around than going back and forth from the lane to the ancient camp.

Laser - Rocket is a ganking build for killing enemy heroes early game. You'd pick this when the opposition has several squishy heroes and/or your team has an aggressive line-up.

The march build (usually Rocket - March) is for pushing/anti-push, or for ancients farming. The combination of rockets/march is incredibly difficult to push against once you have Boots of Travel.

P.S - might make more sense to post these questions over on the forums rather than as a blog.