Depends on what type of work is your primary focus. There are several really terrific rendering plugin's for Rhino out there. So, without knowing a little more about what types of projects you take on, here's a list of some I'd check out. And I'll be the first to admit, I'm a little biased here, as I've personally used all of these in the list below and have a favorite, so I'll discuss why a little.
Maxwell - amazing render quality -- however, to be honest, it's too slow for animation work, unless you have a LOT of processing power. But, some of the most photorealistic images out there come from this program. CPU and GPU options here. http://www.maxwellrender.com/
Vray - awesome render engine, very popular, great for stills and animations. With the latest version you can use both CPU and GPU. It is my understanding that development has gotten a little slow, at least for the Rhino plugin. If you do lot's on interior work, this is probably the one to go with right now. If that's not the case, read on. https://www.chaosgroup.com/
Octane Render - this is my personal favorite and what I do my work in. GREAT for product shots and animations and exterior architecture shots and animations. It does a great job with interior shots as well, however, with Vray you'll get a faster interior rendering vs.Octane. The plugin developer, Paul, is very responsive and listens to feedback from the Rhino community. Material creation is very easy and fast, and there are very few settings to tweak for final render quality. This engine is GPU only. It's very easy to use which is why it's one of my favorite engines out there. I don't think about settings, I just create. One thing to note here, is that with the next version of Octane, they will supposedly integrate Brigade into the core, which will make rendering extremely fast. https://home.otoy.com/render/octane-render/ And here's the brigade engine I mentioned: https://home.otoy.com/render/brigade/
Thea Render -- great quality here as well, both CPU and GPU. Development has been very slow. I followed Thea for quite a while using the Rhino plugin and eventually just gave up to be honest as it was moving at a snails pace. Everything else was maturing much faster. I can't think of anything that Thea offers that Vray or Octane don't. But, it's still worth a look and might fit your work mindset the best. https://www.thearender.com/site/
Personally, if I were you, I'd download a couple of these, or all of them, and try out the evaluation versions. See what program works best with the way you think. Watch some online videos and tutorials. While I don't think you could go wrong with any of these, if animation is your key reason, I'd really look hard at Vray and Octane. And I'd also really look at GPU rendering (vray has both, octane only GPU) as I think you'll get a much faster frame render time if you have a nice GPU system (unless again, you're doing primarily interiors, then CPU is probably still your best bet).
Hope this helps,