smoothness

[coolair]

Still looking on what printer to buy... V2.. probably..
looking at parts that were printed, why are some so smooth compared to an other part about the same size..

does-it have to do with the material used..?

[Polygonhell]

Depends what you mean by smooth, but general quality is dependent on a lot of things
In no particular order

Slicer settings - Layer Height, Temperature, Speed, etc etc
Material
Printer Calibration
Quality of mechanical construction

Very few printers today are really plug and play, there is a lot of messing around to get to great prints.