It depends on the map, but double cap starts are rather rough these days because of corvettes...basically, whoever spams the most corvettes early game wins...
The only reason you'd lead with two marzas is because you are extremely close, and if you're that close then it's pretty much all corvette rushing...if the other player does not invest in a 2nd cap, they will be outdoing you substantially in firepower and fleet size...you won't damage their HW enough with raze planet to make much of a difference....the corvettes will be all over you, forcing your marzas out...
As of v1.02, you're better off rushing with corvettes and gaining the upperhand...then, if you need to wipe out planets quickly (like, knock out a suicide player), use a marza as your 2nd cap...
For TEC, akkans, corsevs, and sovas are really the only viable openers, even on a cramped map...
That being said, this assumes you are going against someone who knows what they are doing...against a noob, a double marza rush will kill them more efficiently than any other start simply...but think of this as more "getting away with" a double marza start...
