What workout is best?
What exercises burn the most fat?
What workout will build the most muscle?
All of these questions will lead you to become demotivated if it's where you start and finish.
They seem like great questions and a reasonable starting point.
So why can they end up demotivating you?
Because they treat exercise as a means to and end, rather than an end in itself.
These questions must be coupled with a primary focus on what exercise gives you immediately; improvement of mood, increase of energy, stress relief, a sense of accomplishment, etc.
Even the “best workout plan” won’t be motivating enough to make exercise a priority, because the benefits will take months and maybe even years to achieve.
So how do I stay motivated with my “best workout plan”?
Focus on the benefits you're receiving from it today.
We’re wired for immediate gratification, so use that toward your advantage by making the immediate rewards(mood, energy, stress reduction, etc) the goal.
If you do that, you have a better chance at staying consistent with that workout plan long enough to see the long term goals you had originally hoped to achieve.