We don't have your data, so I cannot give any examples. As well, I don't know your definition of a smooth curve.
Do you want a curve that smooths out what appears to be noise, yet is fariy simple? In that case, I would use polyfit. Or if you just want a plot, the basic fitting tools on the plot will suffice. A quadratic or possibly a cubic polynomial (at most) fit will suffice. Do not go higher order than that, however, as you will start to get degeneracies, and over fitting.
Do you want a curve that interpolates the points exactly in some way, yet is still smooth. For this, you might want to use an interpolating spline. However it lookes like you MAY have repeated x values, with multiple distinct y values. That will cause problems. And an interpolating spline through data like that will surely look nasty.
Or do you want some sort of smooth curve that follows the points around in the order they are stored? Again, a spline can work here.
Do you want some sort of function you can write down? Or do you just want a nice plot? Do you need to be able to evaluate the function, but not need to write it down?
Regrdless, without your data and knowledge of what you really want out the end, it is difficult to much more. Otherwise I would be forced to write a small book.
