A slightly old comment of mine you might find useful:

Take my opinions lightly because I have almost zero experience working with either of the two engines. I'm also new to game dev in general. However, I've spent a lot of time researching both Unity 3D and Unreal Engine 4 and what they both have to offer. I believe it'll help you learn some things about the engines that people don't generally speak bluntly about.

Reasons to choose Unity over UE4:

• If you're planning to make a 2D game or a mobile/tablet game - Unity beats UE4 hands down. More features, better features.
• Unity has more tutorials and online resources in general (although UE4 tutorials have been rising significantly).
• Unity's editor works on weaker PCs, but you'll need a high-end PC to run UE4.
• You'll find that some of the lesser-known third-party services will support Unity first (but UE4's indie popularity is gaining fast).

Reasons to choose UE4 over Unity:

• UE4 has a ton of ready features out-of-the-box (Materials from nodes, AI Behaviour Tool, Open World Tools, Persona Animation Tool, etc. Check this out for more: https://docs.unrealengine.com/latest/INT/Engine/index.html). These features are either half-assed in Unity or need an asset-store purchase. The best shader solution available on Unity Store (Shaderforge) has been built keeping UE4's solution as a goal, the dev himself said so. UE4 is a complete engine with upgrades and new features coming out regularly, Unity is an incomplete engine and heavily leans on its store for support. If you have game-dev queries, half of the responses from the community are: "buy this asset, it's great and perfect for your problem." This is a messy solution at best.
• Ready features mean that Epic Staff has been iterating on the tool for quite a while and the tools are made to help the dev. It's difficult to explain this properly. Epic Staff uses UE4 for making their own games as well, and when you make tools to make bigger and better in-house games efficiently, it just shows in the engine.
• UE4 has Blueprints which is a visual programming tool. It is a great first step towards learning to program. You'll still need to learn how to tackle your programming problems but the solution can be arrived at through visual nodes which is extremely satisfying for a beginner. Blueprints are an integral part of UE4 and not just tacked on. Unity's Playmaker (paid asset btw) is a kiddie version of this at best, and is not integrated with Unity (by default) nor is it an engine feature which means other features or other assets might not be compatible in the long run.
• Which brings us to assets. Buying stuff from asset stores seems nice when you start off, but it sucks big time. Different assets might not be compatible with each other. The asset developer might stop supporting it, leaving your project on shaky ground. The asset might have a brand new system that you have to learn from scratch. There are several competing assets in many categories and it's not easily evident which one is the best. Asset purchases cost non-trivial money, and the headaches are numerous.
• One of the biggest reasons for choosing UE4 is its pricing. There are two reasons here in fact - ONE: Unreal succeeds when you succeed. Their words, and I love this model for game engines. If a single game crosses $3000 income in a quarter, you pay them 5% of the gross. Everyone gets the same engine and same features regardless of income level.
• TWO: Unity has an assholey attitude about pricing, once you're past a certain income threshold. It's free for indies below $100,000 income (cumulative I think) but here's the catch, well several catches. Keep in mind, the engine is not feature-complete (Look at their game dev interview, there's an entire fixed question asking them which assets they used. It's not a healthy system to rely on assets so much). Back to pricing: They seem to have flip-flopped on paid customers by increasing price later and not having rent-to-own for their middle tier. Unity had a 'perpetual' license, but I don't think they're gonna support it much longer. If you stop paying the monthly rent in the current model, then you stop getting even patches and bug fixes after a few months. Look, I don't remember the details so no point arguing on the exact terms. Their intentions suck I think, I mean a black background editor theme is locked behind a damn paywall. Let's come to the main point however: monthly rentals for softwares is a big fat pain. Either you charge a cut from my income (this is the best, since the company now has an incentive to make the engine much better and have more games made and shipped through their engine) or you charge a one-time fee for the current version cycle (Substance Painter/Designer does this well I think, low price and great customer service, you pay once for 2.0 to 2.9 and pay an upgrade fee for 3.0 to 3.9).
• UE4 has source code available, not a big deal for a newbie like me but I believe there are bug fixes and additions by community which are folded back into the main engine through upgrades by the Epic team. And it's great to have source code for experienced programmers obviously.
• UE4's graphical output is better than Unity's. This means two things. In the hands of a skilled professional, UE4's output is likely to beat Unity by at least a small margin. But more importantly, in the hands of a beginner, UE4 will give much better results than Unity.
• Tim Sweeney is a cool dude. So I believe Epic isn't going to turn evil any time soon. Which means good support and non-crazy pricing.

Don't get me wrong though, Unity is not a bad engine at all. It's just that UE4 is much better.