This kind straight handles
or this kind?
Stack Exchange network consists of 181 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.Visit Stack Exchange
Bicycles Stack Exchange is a question and answer site for people who build and repair bicycles, people who train cycling, or commute on bicycles. It only takes a minute to sign up.Sign up to join this community
Right size for you. A must.
Light weight as possible/desired
Low price - it needs to be do a simple job without being a thief magnet (at least here)
The difference between handlebars, or in general body postures on bicycle, starts to show itself at distances of 50 km. For 5 kilometers a day, which I assume consist of two intervals of 2.5 km each (to work and back), it really does not matter. I would say gearing would play more difference than type of bike.
One style of flat handlebar is not absolutely better than another. You should test ride some bikes and see what you personally prefer.
Bicycle stores offer test rides in the USA, but I realize it might not be the case where you live.