Iron "pro": lollipop, 3go Ram but processor octacore 1.3 ghz and good camera
Emax: kitkat only ! 2go Ram, processor octacore 1.7ghz, battery 3800 mAh, no good camera...
The Iron pro is the Best (in the spec, for me)
there is not necessarily a good follow , but the devices are of good quality , so I recommend the last out , to have the latest version of android
If the performance and/or battery life is the most important for you, then eMAX can be your choice, despite its relatively obsolete Android version. The less amount of RAM doesn't really affect the performance (not even if you've got a hundred large apps installed) but the faster processor does it. The average battery life is much longer then that you would expect from a such slim smartphone. Another selling point of the eMAX is the extraordinary good quality headphones output.
The Iron Pro is built with a definitely better quality camera. There's a flash light on the front side too as an addition plus the fingerprint sensor on the back. That model still offers quite a good overall performance and battery life but there are issues with the headphones output. That depends on unique taste, but the design of the Iron Pro looks better in sight of most users. Moreover, you get an up-to-date Android 5.1 system with the Iron Pro.
So, definitely these two phones are the best models of UMI but you should decide which parameters are the most important for you.