I have done a lot of experimenting with the best way to ensure first layer adhesion (Lulzbot TAZ 6). I have found the options in the Simplify3D code very flexible, and allowed me to try may options - including slightly lowering the Z axis to force the filament into the bed, having different bed temptation forfeits layer, and simply printing layer 1 200% thickness.
Of all of these, the most successful to date has involved deliberately feeding more material for first layer, in my case a multiplier of 1.75, but not changing the layer thickness. This has two effects - firstly it seems to ensure good adhesion, and secondly it forces the layer to appear very flat and smooth when removed from the bed rather than showing the gaps between each fill path.
I have had to set this up using two process stages, one for first layer and one from 0.2mm onwards. It would be nice if there was a simply first layer extrusion multiplier option in the Layer menu so this can be done without having to set up two processes.