As a solo dev (in my spare time) UE4 wins hands down, more tools/power in one package. You can actually spend less time working around engine shortcomings and performance problems. Been using Unity professional since 2.x days and in fact still do in the day job and on contracts. its a fine engine but you need to learn a lot of tricks and work arounds OR spend $$ on asset store things to help. Those of course tend to vary widely in usefulness/appropriateness.