
Is quality better than quantity? That is a tough question to answer as there are plenty of different ways to look at units and there usefulness.I will not be going over any particular unit, just a generalization of a group of units that function similarly to each other. Lets start with quality units, the power-houses of an army.
Quality units are generally the unit that is expensive but can dish-out the pain. They can also be classified as the do everything unit. Such units would be nob bikers, seer council, thunder hammer terminators, trygon, ect... The one problem that becomes apparent is that you cannot field very many of these guys as they cost a lot in points. So losing these units would be a heavy blow to the army.
The quantity unit, however, is usually made of poor fighter units, made just for the propose of dying or holding a particular point. Units such as these would be Guardsmen, Guardians,gounts,Ork boys ect... These guys are only scary in numbers and not much els. The thing that makes them strong, however, is there low point cost. A low point cost gives these quantity units the ability to just be "pawns" in you game. So losing these models wouldn't make you sweat to much.
But both of these types of units suffer from one thing... the board. Quality units generally are very small, so there influence across the board is small. and quantity units generally "overcrowd" each other. making deploying and moving around tough. I made the mistake of taking to many units.
I went to a terniment once for 40k and had the idea that an all quantity force could stop any quality or mixed force. What happend was that the ternimant, being only 750 points, used smaller boards then the normal size. I couldn't deploy strategically at all because I would just run out of room to deploy, giving myself no say in where my men whent. The only armies I was able to beet were the elite armies and even then, only because I was lucky.
On the other hand, my brother with a mixed force, ended up wining the terniment. Why is that? He had numbers to control the board and small elite units to keep his opponents attention.He didn't have 80 guys on the table to congest him, so he could deploy with some finesse.
So is quality better than quantity? No, it is better to have a good mix of the different types of units supporting each other. otherwise your small elite units will get isolated and destroyed or your swarm will get over crowded.