You don’t want to perform a job and then get to a point where you are saying “Shoot, I need a 3/8 for this.”  Get both - cover your bases, as they say.  I even have a 1/4 set.

There are good reasons why there exist different drives, … like 1/4, 3/8 and 1/2.

If you serious about doing your own work on anything with bolts and nuts, owning all three is highly recommended. Large bolts and nuts - large torques - large drive. Middling size, middling drive. Little ones, little drive. Go get ‘em all three, … 

F.S.

1/2" sockets and ratchets are good for larger size bolts that are easy to get to, like the bolts holding the shocks to the rear axle of a truck, or a differential plug if they're that size, but they don't always work in tight areas because they're pretty large. In my experience, my 3/8" drive and sockets get way more use than the 1/2" set. The smaller size sockets also aren't available for 1/2" drive, you'd need an attachment to downsize the socket, which is a little redundant. You can always make a 3/8" socket longer by sticking a hollow tube over the handle and using it like a cheater bar.  

Get a set that has both. It's better.

I tried to get my with just one size and an adapter to change sizes. While it technically works, the cramped working spaces of engines yield adapters useless. I ended up getting another set so I could have the size that I need when I need it. 

Scotty answers your question at 6:51 below

https://m.youtube.com/watch?v=0YToSmz1Qb4