What breed is better for someone who never owned a dog before...A Labrador or Rottweiler ?

A labrador obviously and I'm sure you know this being a regular troll on here. 

A Labrador

Omg a labrador.  They’re so chill and easy.  

In your specific case, no dog is better than any dog.

The Lab.  It has been America's number 1 favorite for over 30 yrs.  The Rott would need an experienced owner with a firm grip on knowledge on how to handle such a dog.  Not for a first time dog owner.

AS if you didn`t know  already  ................Anyone with just half a brain would know its a Labrador.🙄🙄

a gentle labrador. They are very loving.

Lab is easier as first dog. Depends upon your activity level, dealing with fur and shedding, yard and home space, about children in the household if any, and whether you want to train and play.

I had a border collie/black lab mix. Smart, friendly, long life, just quick and active enough, loved to please, loved attention.

Shed like crazy, long black hair. I had her for 17 years. 

I prefer mutts over buying from a breeder, taking the chance while rescuing a dog that needs a home.

 Border Collie: prized for its intelligence, extraordinary instinct, and working ability. Bred to work all day, so you have to give him/her attention and play a lot. If you have kids, border collies may start to push them around. They win the staring contest also. If you don't have the play time, skip Border Collie.

Golden Retriever: Intelligent and eager to please. Almost always a happy dog. But heavy shedding and very "mouthy" likes to pick up things and carry them around. Needs brushing and teeth care regularly.

Labrador Retriever: An ideal sporting and family dog. Gentle and intelligent. Most domesticated dog. Does need and love exercise, and not just a walk around the block. 

Rottweiler: Robust and powerful, the breed is happiest with a job. Devoted companion. Some over-aggressive lines out there. Heavy dog that likes to sit on your feet or lap. Can get aggressive to other animals.

Having a smart dog is like having a smart kid. If you don't give enough attention they figure out a way to get into trouble.

Beagles and Jack Russells tend to do what they want to do.

Bulldogs are lazy. You have to push him to go out to stay healthy. 

American Staffordshire Terriers (Am Staff) are powerful, looks like a pit bill, can be stubborn, and sometimes like a clown. They each have a unique personality. Not a good first dog.

First dog you have the good and the bad. 

The good is that it's having a child and best friend living with you whose main purpose in life is YOU. 

The bad is that it's like having a child. A dog needs and demands attention and exercise. If not willing to give him/her your attention, then don't get a dog. The dog becomes a family member. There are differences between breeds, but also, like people, different from each other. Look carefully into best dog treats. Don't play the pull game with rope toys. They love tug-of-war, but never stop. The throw fetch game is better. They run and come back. Much less work. They also get possessive about their toys sometimes. Teaching "Drop-it" with a tennis ball is first challenge.