I've printed a 2x2x2cm test cube with Slic3r (left) and Cura (right) and my Prusa i3 derivative machine with tight belts. The print settings should be quite equal (0.15mm layer height, 40mm/s outer wall speed, default accelerations/jerks). Though the top surface of the Cura-cube looks much better than the Slic3r-cube,
the latter has much flatter vertical walls than the first.
The front wall of the Cura-cube was printed from left to right which could explain the wavy result as some kind of vibration caused by the sharp y-stop at the left front corner.
But what setting could have influenced this? Should I try to manual setting of lower accelerations in Cura?
Those wavy lines could be artefacts caused by closely-spaced infill, but they could also be resonance patterns caused by noisy stepper motors and over-tight belts. Since you have said that you have your belts nice and tight, I would suggest reducing the tension on them and see what happens. I know that some pundits say that it is not possible to have timing belts too tight, but I disagree with that. Belts should obviously be tight enough to eliminate free play in the system, and you may have a lot of latitude in the tensions that you can use, but if you make them drum-tight, they will transmit motor vibrations very effectively to the build plate (and onto your models).
If your stepper motors are noisy, you may want to invest in some vibration dampers. They can reduce noise and vibration significantly. Another solution would be to use more sophisticated stepper motor drivers, such as the TMC2100.