A fine blade and the more teeth the better. The main thing to bear in mind though is that a circular saw cuts on the UP stroke so if you were to try and saw it laminate side up, as the cutting blade comes up through the work top and reaches the laminate, it will chip it away from the worktop board.
So you cut it with the laminate face down so as the cutting blade comes into the laminate, the laminate is supported by the worktop above it and doesn't chip. You could also put some masking tape on the laminate cut line but with a fine blade and cutting up into the laminate you shouldn't need to. If you have some spare, try a practice cut first.
Just be careful when cutting with the worktop upside down that what you are resting the worktop on will not scratch the laminate.
On occasionally I cut with the laminate up. I clamp a straight edge to the cut line and gently score along the edge (gently a couple of times) with a sharp Stanly knife, then pressing a little harder three or four times.
I then finish off to the line with an electric plainer.
Scoring around a curved edge takes a bit of practise, but can be done.
If cutting out a hole for the sink/hob, cut with the worktop laminate side up, and use a downward cutting jigsaw blade. I also use a wide piece of masking tape to draw the cut line on and to protect the worktop from being scratched by the jigsaw base