Hi CountryGolden,
I have quite a bit of experience with Thea, Octane, Maxwell, and Vray (older version of Vray, not the latest).
Bottom line is what you probably already know – each has it’s on strengths and weakness of course and I think it depends on the type of work you are primarily doing. Below are my thoughts, and like everyone I have a favorite too and it’s Octane.
Maxwell – I think it’s the highest quality output, most photorealistic. The others are not far behind though to be honest and with a hair of post work the quality differences start to disappear between all of these engines. However, it’s still quite slow compared to the rest, even with GPU integration in the latest version. If you are primarily doing work that requires the utmost in photorealism and you are not wanting to do much postwork AND you have the time to allow for long render times, then Maxwell is a good choice. It’s integrated fairly well into Rhino and it’s very easy to understand and learn. If you have any kind of background in photography (I did) then you’ll pick up Maxwell quickly.
Pros: Photorealism, easy to learn
Cons: Slow, Slow, Slow render times
Vray – I’ve only had experience with V1 and V2 of Vray, but V3 has a LOT of improvements. From what I can tell and from talking with other users, Vray isn’t as hard to learn as it used to be. There used to be a long learning curve, but I think the latest version has solved that. Vray’s quality is outstanding and it’s highly customizable. It’s a very mature render engine with a lot of features. I think the strong points of this render engine are it’s ability for large output renders (CPU capability), Tweakable settings, Clipping Planes, and Vray Fur/Grass. Since it has a biased mode you’ll (usually but not always) get a faster final result on interiors.
Pros: highly customizable, great quality, CPU renders for large format output, Fur/Grass
Cons: to get into the highly customizable settings there’s still along learning curve, if you stick with basics it’s easier
Thea – Terrific Quality with this engine and it’s various modes (CPU and GPU) are great, same as Vray. Learning curve wise I’d say it’s easier than Vray, not quite as easy as Maxwell, but close. Render times are much faster than Maxwell, not quite as fast as Vray. You said you’re familiar with Thea so I won’t go on about it, but I do think it’s a great engine. The reason it’s NOT my primary go to however, is because the support has been very poor and the development of the Rhino plugin has been at a snails pace, REALLY slow. This engine doesn’t really offer anything that the others don’t right now and since support for the Rhino plugin has been so lacking, I’ve pretty much dropped Thea from my daily use.
Octane – as I’ve already mentioned, this is my favorite engine. Octane, to me, was as easy to learn as Maxwell. It’s settings are clear and straightforward and there aren’t many to deal with. Material creation in this engine is very flexible as you can mix materials quite easily. Has a great dirt texture for mixing materials as well as a nice amount of procedurals for flexibility. Has an Unbiased mode (Pathtracing) and a Biased mode (Diffuse and AO). For just about everything but complex interiors, the render times with Octane are super quick. Complex interios aren’t a problem to do, you’ll just notice a slow down compared to the other types of renders with Octane. However, I do think this is a Con to any unbiased engine. There are some improvements with the latest version of Octane that are making more scenes with indirect lighting faster though. At least with my system, I can achieve much faster final renders with Octane than the others. My system however, is a GPU oriented system, not a CPU heavy system, but all the renders on this list have GPU modes. The main con to Octane is that it’s GPU only. This really only matters if you are doing an enormous renders that can’t fit on your GPU though. I haven’t had any issues with this, but some users do. Again, depends on what type of work you do and of course what kind of hardware you have. I have 8gig GPUS and don’t even come close to tapping them out. Development is very fast with Octane and the developer for the Rhino Plugin, Paul, is simply amazing. He listens to the users and does his best to accommodate requests. Support is outstanding. Another Pro for Octane is that the next Main version will be integrating Brigade (a near real time render technology). This should make Octane render insanely fast. Check out Brigade on the Otoy website if you want a sneak peak. Quality is outstanding with this engine. I do quite a bit of animation work and Octane is well integrated into both Rhino and Bongo – that, along with it’s super fast render times and outstanding quality, are why I use Octane 90% of the time.
Pros: Amazing Support, Great Integration, FAST render times
Cons: slower than Vray on interiors, GPU only
Anyway, I know this was long winded, but I hope it helps. I could keep going on about each engine, but I’ll stop. I honestly think these are all strong render engines, but I think it ultimately depends on what type of work you do. If I were you, I’d download and try out the ones your interested in, give them a spin, and see what fits you and your work type the best.
Ryan