On consoles, Unreal Engine is probably the most prominent, if not the most popular, multiplatform engine powering games, thanks in part to its ability to deliver high-end visuals in 3D games.
On mobile, however, with both the full-power engine and the more indie-friendly Unreal Development Kit, it offers similar capabilities, but hasn't managed to amass the same level of popularity that Unity has pooled.
Part of it is down to the flexibility of Unity engine's. It allows for rapid prototyping of games. It is capable of high-end graphics, in particular Madfinger's library of titles. It is also becoming increasingly viable for two-dimensional games, thanks in part to its community-driven plugins.
It's got to the point where the engine is being used not only by one-man teams -such as in the case of match-3 RPG 10000000 - but also established players such as Rovio with Bad Piggies.
UDK has not seen the advantages that Unity has. It's reportedly much harder to get games set up and going with it.
There's less of a plugin community, though one developer I spoke to, Chris Murphy of Pub Games, who recently released the Unreal-powered BlastPoints to iOS, said that the studio had managed to pull in support from "a range of other developers and Epic themselves to overcome various issues or to implement extensions to the engine."
However, a big part of the problem for those looking to develop cross-platform title is that UDK is not actually that robust of a mobile solution.
The platform only provides support for iOS and PC to release on other platforms requires access to the full Unreal Engine license.
Also, UDK offers many of the same tools that the full Unreal Engine offers, minus access to the source code. In comparison, Unity offers its tools en masse to anyone who downloads its engine, and those who pay for the licenses to compile for different platforms get those abilities out of the box
Will UDK ever come to Android? It's looking unlikely. Games that use Unreal are already available on Google's OS, such as Dunegon Defenders and Gameloft's Wild Blood. But said titles aren't actually written in UDK, which still doesn't compile for the platform. they aren't being made in UDK, which does not compile for Android still.
Why we're still waiting is a mystery. Epic VP Mark Rein said back in April 2011 that Android support was coming to UDK. Flash forward to 2012, however, and nothing's changed.
This is despite the expliclty-mentioned file size limit having been solved by Google supporting external data downloads uploaded to the Google servers.
UDK's pricing is also a major concern for developers.
There are plenty of games that use Unity and don't make the jump to other platforms, though the option is certainly there for developers.
For these studio, the relatively flat pricing of Unity may be extremely appealing. The core engine is free, with Unity Pro available for $1,500, and addons running from $400-$1,500 USD.
While the entry price for UDK is a reasonable $99 for commercial use, a steep 25 percent royalty kicks in for anything above $50,000. This alone turns off some from working with the engine.
For example, Josh Presseisen, CEO of publisher and developer Crescent Moon Games said that he'd "much rather pay several thousand for a Unity pro license, and never again have to pay Unity another dime, rather than worrying about paying them a pecentage, which is how Unreal's terms work."
Presseisen represents an interesting perspective on the issue: he has worked with several titles that use each engine.
Wraithborne, published in Ocotber, uses UDK, and the upcoming Ravensword: Shadowlands uses Unity, and will launch the same day as Last Knight, which is built on Unreal.
"Visually, I believe its 'easier' to make games look better with Unreal," added Presseisen.
"I believe Unity is just as competent, but you need to work a bit harder to make it look good. The workflow for Unreal sometimes favours a larger programming team, whereas Unity allows you to work with one programmer, one artist - which is often the case in most of the Unity games that I've published - with the exception of Last Knight developed by David Hagemann of Toco Games."
While many games struggle to reach the $50,000 revenue point using either engine, the break-even point for small teams - even on 2D games - may be into the six figures. As such, giving up 25 percent of the revenue is a hefty slice after Apple has taken its cut.
'Equal playing field'
Unity's biggest advantage is simple: it's set up to keep developers on an equal playing field from the start.
The mighty Rovio hypothetically pays the same for the license it used in Bad Piggies as any others that tap into Unity - and the engine covers platforms aplenty beyond iOS and PC.
Indeed, the fact that Unity is so level mirrors the theoretical potential of mobile app stores: everyone can use the same engine and get equal space on the store.
However, there has certainly been an uptick of games published with Unreal and UDK. Gameloft is now a notable backer, with Wild Blood making waves.
Even independent titles such as Wraithborne and ARC Squadron have been made in the engine. Pub Games' Chris Murphy said his studio went Unreal for BlastPoints because the firm was "already pretty well skilled with PC development and Unreal Engine so this was a natural progression for us technically.
"In addition to this, we knew Unreal so we were able to work to the strengths of the engine and within the limitations so we knew we could get it looking great and performing pretty well," he added.
Really, that might be the future of Unreal on mobile: as more console teams start to explore mobile and what it can do, there's a good chance that the engine will pick up in a significant way.
Nonetheless, Unreal is clearly at a disadvantage right now. Epic may be a top choice on consoles, but its lack of initiative on mobile is clearing hurting the company.
Presseisen has some advice: "In order for Unreal to reign supreme in terms of snatching up the lion's share of developers, it is going to need to come up with better licensing terms, and more frequent updates to its system."
Whether Epic actually plans to appeal to developers as an alternative to Unity, or continues to largely just exist for the sake of existence is still quite a mystery.