If I would have to choose between Unreal or Unity I would choose both There are strenghts and weaknesses of both engines, but from my experience:
1. Unreal is a nice package "out of the box" - you have your post-processing tools, volumetric lighting, nice skydome and lighting, node-based material editor, good import of static FBX files and they work hard to make better integration with 3ds max with Datasmith.
It is widely used, has really good forums and many eye-candy visualizations were made with that engine. It's capable in this field and proven. You can also sell your scenes without hassle - it should work at the clients side as on your side in the given Unreal version.
Weaknesses: not-so-friendly camera sequencer (but it does not matter unless you make some truly cienamtic-grade stuff), really messed up import of animations, not to great particle system (and hard to edit), no integration with Blender files and non-modularity (most of the things that you find on Unreal Market are assets, plugins are rare and they do not extend Unreal capabilities).
It's closed system. What you install is what you get,l it will not get better unless they make an update.
2. Unity: out-of the box is stripped down of many features, luckily there is TON of simple add-ons (many of them free) that can make it look on-par when it comes to graphic quality of Unreal. It has great lighting, realtime GI with Enlighten, new Progressive sampler that works really decent, easy to use sequencer (and four more that you can buy from store), good post-processing stack (in my opinion much more user-friendly than the one in Unreal).
It is easier to learn (subjective matter), it accepts everything you throw at it (FBX, OBJ, Alembic, Substances, blend files, animations), it updates assets automatically - no need to constantly "reimport" things, it is modular - which means that you can have better post-production, camera filters, better antialiasing, reflections, camera tools, etc with just few clicks.
It launches much faster than Unreal and almost none of the operations require restarting the engine. A great knowledge and userbase. And they are going into cinematic / visualizations bussiness also. It has already Octane integration in-engine.
Weaknesses: you have to gather some nice plugins to make it shine, luckily Asset Store + forums are doing a good job with that. Not so good: many things will cost you some bucks, but generally they are worth it. No node-based material editor in vanilla version, but you can get one from Asset Store and people say it is comparable to the Unreal material editor - i tested it too short to be an advisor on that matter. Selling scenes is difficult, if you rely on third-party plugins - you cannot include them in your project AFAIK so you cannot transfer the scene to the client with the same quality.
I use Unity for my personal projects and we use Unreal in our company - so I can say that both of them make a good work.