I started out with scanline and after a while started getting some nice renderings. Then I tried to render a big scene, and there was no way the Viz default scanline renderer was doing it, the file ended up way to big and would always crash the pc (64 bit and 8 gig ram might have solved that but it was before that). Looking for solutions I started to read up on the different alternatives out there, and there where many ... I ended up trying mental ray, because it was free, it was already in Viz and I didn't even know it existed Everything was looking good until some black weird spots started showing up and my RPC was not working ... Then I started once again to look at other options: Brazil, Maxwell, Vray, etc.
I tried out Brazil and it seemed very similar to mental ray but for that I rather use mental ray. I kept reading in alot of places and seeing many sites (evermotion, cgarchitect, cgtalk, vismasters) with people showing their very nice renderings and they all had one common denominator ... Vray. One thing that caught my attention is the quick lighting preview that you can get (something I really wish mental ray had), maxwell I think has it too. The thing I am most interested at the moment is the Vray Stand Alone which hopefully some day will be released. One thing that I didn't like about Maxwell is the 4 processor limit per license. But at the end of the day it's like comparing Revit and Archicad or ADT, it's one of those unending discussion.
I think that one should use whatever works for them, and it's always a pain to take time out to learn new programs, I rather get to know really well the ones I use most often. And more and more the different programs "borrow" features from one another, so Maxwell and Vray may end up with many similar features. You use "(Though honestly I only use Mulitlight on interiors, for exteriors I have my favorite sun settings.)" I use the sun/sky for exteriors in Vray and for interiors I just override the environment with a color (turning of the sky) and then raise the multiplier.
Apart from renderers ... for trees I ended up with Onyx which look good and have the random seed option which is very nice and am looking for cars at the moment. Dosch cars look nice.
In the end be it Mental Ray, Maxwell or Vray I think we can agree on one thing ... Accurender in Revit is light years behind .... Hopefully plugins for Revit will start popping up someday like they are for Archicad now.