In a few minutes this video gives a summary of the differences (and similarities) between the 3B and 3B+ versions of the Raspberry Pi from the point of view of a reasonably well informed and hopefully impartial user. Nothing spectacular, because much of this information is often seen or heard already here and there. The object of this presentation is to put them to a comparative test, starting the two versions simultaneously, followed by a comparison of their performance, particularly their power consumption. The tests start by timing the installation of Raspbian (with Noobs 2.7). As you’d expect, every second counts!

A snapshot gives a clear picture

The result of the comparison of write times (to two identical SD cards) is worthy of attention (even if it’s taken with a pinch of salt).

But like most comparisons, it’s not exhaustive, nor does it pretend to be. It’s only a snapshot, but a fairly clear one. The options for improvement on one or the other version are in fact so numerous that it would be a waste of one’s time to try to get to the bottom of that subject.
 

In the end, it comes down to you making your own choice taking into account your criteria and requirements. Don’t just look at your actual needs, but also the possible evolution of your design. The little + sign that marks the difference between the old and new models isn’t just there to attract your attention; it does represent real progress.