Printing solid is more difficult. The reason is if you are over extruding more than a small amount, you will have problems with top surface quality because the nozzle will be dragging across the surface as it prints leaving unwanted marks and depressions. It will also tend to make the print over sized in X-Y because the plastic has to go somewhere so it squeezes outward and make holes smaller. The reason the plastic has nowhere else to go is there are no partial layers underneath to accept the additional plastic and provide some cushion
Of course if you under extrude, you will have all the problems associated with under extruding, gaps and skipped details, etc.
So you have two choices, spend a lot of time getting your printer tuned to perfection. Or, print with something like 50 to 75% infill instead, which, if you over extrude, will not be a problem because the extra plastic will have somewhere to go, other than out and up. At that high of an infill on a machine that is over extruding a little, it will essentially be a solid part.
You will want to tune your printer reasonably well in order to get a good top surface finish. So I typically aim for slight over-extruding so I don't get any gaps anywhere, but not so much as to hurt the top surface.
Some people use a technique called ironing to improve top finish quality, but S3D does not support this capability yet. Other slicers can do this.