Personally, I hold off entirely on shields until I've acquired the first several armor techs. The primary reason simply being that low level armor will take up an obscene amount of HS on even modestly armored vessels.
Can't contribute much to the debate about the effectiveness of armor/shields as I'm fairly inexperienced myself, but I'll give an example of a decision that I'm currently facing: On my 20k ton flagship, my initial design accounted for armor with a thickness of twenty. However, if I were to drop the armor down to sixteen, I can fit in seventeen shields. If I drop the armor to twelve, which is still pretty damn thick, I can up the shields all the way to thirty-five. This part of the debate is only taking into account the HS that was initially earmarked for armor, so I will probably be able to throw even more shields on the vessel.
Unfortunately, I don't currently have the shield techs researched and the wiki is rather lacking on data re:shields, so I can't really formulate a proper opinion on the theoretical effectiveness of my design quite yet.