No one is trying to be mean here, well maybe Keesha and Drive on, thats just a little sexual tension
What you need to realize:
a) Queso is not Mexican - its Tex Mex(like has already been said) and was developed not all that long ago. It was developed after the super processed cheeses hit the market had already been created. They are the original recipe. It easy with those cheeses as compared to using "fresh/normal" cheese
b) you can not just plop some shredded cheese in a pot and hope to have anything edible
you really have to either start with a veloute or bechamel (think like the base for my Mac and Cheese - but with more cheese) - or you gotta go with the velvetta and co.
Velveeta and the like are made by adding milk protein concentrate. MPC can make products more heat stable, and it can provide solubility and dispersibility when used (from wiki). This stuff is used to "mimic" the properties of a traditional veloute/bechamel(these sauces take some care once you add cheese)but make it more stable.
What cheeses to use to make it more "Mexican?" Any of the ones listed above (Oaxaca and asadero - is The direction I would lean - but thats preference). Look for soft cheeses think mozzarella feel - you would want to stay away from the dry and semi-dry cheeses they CAN be used but will result in a different texture.
You also want to stay away from the crumbly, fresco style cheeses that dont melt well. Now you can always top you queso with these and I recommend it for texture and flavor - mix it with some cilantro and small diced red onion and it would look great on top. But it will not add anything to the smooth queso texture.
[This message has been edited by bonfirewillburn (edited 2/6/2012 10:56a).]