Microstrip transmission line impedance calculation
It looks like  two simulators you used bracket the value given by FEM simulation of the stackup described in the OSHPark documentation.

 

Here is a simulation of the characteristic impedance of your microstrip structure swept over trace width.

You should remember, as some of the comments on your question point out, that there will be some variation in the geometric parameters of your board during fabrication including changes in line width and prepreg thickness.