You dont necessarily need a beefy system for UE4. I’ve been using UE4 on an i5 3570, 8GB RAM, GTX 460, 120GB SSD since Beta and while i cant get 60FPS all the time i can at least work easily without any trouble.
Thats all i can say on this topic since i’ve never used Unity.
Edit: But wait, i can tell you why i had picked UDK instead of Unity back in the days as a beginner and non-programmer; it was Kismet that attracted my attention. 