I'm planing on getting a desktop computer and wanted an opinion on what specification to look for if I wanted to do 3D modeling and rigging without incessant lag.
I want to Model, Rig, and Animate.(I know, it's a lot to learn but I want to be diverse in skill) and I'm using Blender first.Depends. What 3d software will you be using? Will you be rigging characters and animating for games? Will you be sculpting? How about rendering (again the software and render engine is important to know about: will you be rendering on the GPU?)
In general, get the best graphics card you can afford. Ideally with at least 8GB video ram (avoid Quadros: waste of your money). Get a computer with at least 16GB RAM or preferably more (32GB is better).
But knowing your exact goals will be good to know.