All great insight you got here and it truely does come down to what your end goal is. If you are looking to really get into the mainstream of illustration work, you may want to consider v-ray as first priority. It is probably the most widely used in the industry, fastest, and produces top quality. Now, I am talking about final production work that big arcthitecture firms use and animation/illustration/motion graphics studios use. I know not everyone uses it, but it seems to be the most popular, plus it also is incorporated into most of the big name 3d aps., but there is unfortunately no standalone version. The other thing to consider if you are really trying to get serious about illustration is recognizing that there will probably be a point where you are going to need to make the a switch to the 3ds max, due to the limitations of SU in various areas, and v-ray is "THE Rendering Engine" for 3ds max, but from what I am told v-ray for su is fairly similar to vray for max. For just an architect, you may not need all this and another ap may suite you better, but like I said, if you want to get to the level of huge studios like spine3d or neoscape, you will want to learn v-ray. And if you have the time to learn it, which you will honestly need, the workflow can actuallly be very fast. Vray is more about what settings not to touch as opposed to altering a million different things. I recommend reading through the manual and just start playing with different materials. It will definately be worth it if you ahve the time to put into learning it. But the more apps. you learn the better you are so dont just look for one solution.
