I have both the EagelTac T20C2 Mk II ("ET") and the ZebraLight SC600 ("ZL"). I cannot comment on the other two models you listed. Both the ET and the ZL are great lights, perhaps spectacular in the case of the ZL. The ET can operate on two primary or rechargeable 123 cells or on a single 18650 cell. The ZL only operates on a single 18650 cell. The ET allows you to swtich LED's. I have modules with an XR-E R2, XP-G R5 and two different XM-L emitters. I use the XR-E R2 for excellent throw and the higher output XM-L for overall brightness and flood. The ET is very well constructed and has been very dependable.
The ZL is my current favorite! It is more compact than the ET and the UI is very different. Much has been written about the ZL UI on CPF so I won't spend the time describing it. Nevertheless, I do like the ZL UI very much. It is easy to use and very intuitive. The ZL boasts 750 lumens OTF and I must say I believe it! It is very bright and floody. It also has a very useful firefly level that I really like and use frequently. It is a very solidly built light.
Overall I would choose the ZL over the ET. I like its size and UI better than I like the ET's size and UI. While the ZL is more compact than the ET, IMO neither is the best option for an EDC if you like to carry it in your pocket. The ET is far to big to pocket, again IMO, and the ZL, while smaller, will be felt. I ordered a holster for my ZL from Thors Custom Leather so that I can carry it on my belt when I choose. However, I currenlty carry a ZL SC51 or an SC31, in my pocket for my EDC needs.
Both the ET and the ZL are great lights and I'm not going to part with either one. The ET is more versatile with its different module and battery options, but I would choose the ZL with its wide range of levels, amazing OTF output and UI over the ET if pressed to choose one over the other. For what it's worth...