I need to agree with Sorean that this is a very subjective question since you have not stated what you mean by "better".
If it is simply a matter of how effective it is...then that depends on the race you are playing against, and whether or not it is scouted.
Generally, though, I would say that 4-gate is "better" then marine/scv all-in since 4-gate really isn't an all-in build. Even if you manage to fail to kill the enemy, if you are able to deal quite a bit of damage, you can easily transition out of it and keep the pressure on the opponent for a good portion of the game. If you pull out of the attack after you realize it won't result in a win, you'll be all the stronger.
Honestly though, you should not be using all-in builds. At all. They are fine against lower level opponents, but once you start facing stronger players you're going to start losing more and more of your games, and if all you've been doing All-In cheeses, chances are your Micro/macro isn't the greatest. In other words, relaying on all-in builds is just going to hurt your game in the long-run.