for what it's worth, i've never gone back and replaced a system I've written with a newer Unity built-in system, I just carry on using mine, which is very optimised for my specific needs, so it tends to be simpler and more efficient. 

Unity5 is free, but still closed source. 

The personal edition is also royalty-free, which UE4 can't boast of. Seems like a good enough reason to prefer it in certain cases. 

A lot of people find Unity easier to use. It's got a reputation for that. Also, lower system requirements and more platforms, as far as I remember anyway. 

I've downloaded the latest versions of both the engines, and I'll be playing with them a bit... I've had a little Unity project I've been halfassing here and there with for awhile, but I'm also keen on giving UE4 another shot and wouldn't mind moving to it. The subscription fee was a killer for me before because I only poked around here and there.

My impressions in the past were that Unity is much easier for small teams to just get something basic up and running, but you pay for it later in the optimization work, no source access, etc. On the other hand, UE4 is daunting at first, but better suited in the long term for bigger games, and plays nicer with larger teams.

...there's also Source2 announced, but I'd never touch a Valve engine ever. Too much duct tape. 

Good for everyone that could use an engine. May the one with the best tools/community/documentation win!

Don't really get people who complain about 5% if you're actually making money from your project, think it's a very good deal.

Paid for one month of UE last year just to have a look but couldn't justify paying for more without enough time to learn.

Pay no royalty for film projects, contracting and consulting projects such as architecture, simulation and visualization.

This is also very generous. 

https://forums.unrealengine.com/showthread.php?94470-HammUEr-a-Hammer-Worldcraft-map-importer-for-Unreal-Engine

Been watching this develop on Twitter, looks like they're finally hitting prime time. Convert HL2 and later map formats into UE4 - and they do specifically mention that using Jackhammer and Hammer you can get Quake maps. (Somewhere in the Twitter account you can see shots of e1m1 in UE4).