The Solar shop says they should be in series if sunlight is limited or if you have any shading on the panels, Which will give a higher voltage but the Amp output is the same as it would be for a single panel.
But in Parallel you get more Amps but the Voltage is lower and any shading can cause the voltage to drop below the desired amount,
It is confusing as to which way is better, They make a good argument for both setup's, In series' giving out 7 Ah from 4 X 150w panels is a good steady flow, But in parallel getting 28Ah from the same panels Sounds a lot better but the Voltage is lower on the input side of the MPPT Controller, I think in series should be called Winter setup and in Parallel should be called Summer setup, Or compromise by running the 4 panels in 2 banks of 2 so they are in series and parallel at the same time.
regardless of the above I am still not clear as to which is best