The srt.phone I would suggest. I'm using this currently and it is really delightful! I'm not the heaviest user once can find, but the storage is in surplus for me. The srt is FLOODED with sensors which make the User Experience wonderful. The CoolPad on the other hand lacks basic sensors like Gyroscope and Rotation Vector. Just yesterday I clocked an AnTuTu Benchmark score of 99,321 on my srt.phone. The srt has decent battery life for an average user, but even if you're a heavy user, QuickCharge comes handy. You will not regret the purchase of the srt any day. But please go for official accessories no matter how prices they are. I got a stupid screen guard for 200 because the official one was costly and the screen guard does not cover even half the screen and has costed me my phone's display.
The srt undoubtedly. LeEco on my opinion is a gimmick based brand, with phones having sky high numbers (as in RAM, Cameras etc.) but have absolutely nil optimization and a horrendous skin on Android. LeEco devices are also as fragile as a wafer, my friend lost his phone (Le 1s) with just one drop with a case (yes, literally the whole phone stopped working, losing the ability to boot also) while I've dropped my srt 4 times without a case and it's also scratch free. Srt also has great updates, gets updates sorting many issues on a monthly basis, while you are left for yourself with the LeEco. I'd say srt is the best phone under 20K undoubtedly.
Honor 6x is better in my opinion. I am using this phone and it has nice cameras and lag free performance, good battery backup. However , Smarton Srt.Phone has snapdragon 652 processor which is more powerful but other things like cameras and battery are average. Smartron Srt.Phone 64GB vs Honor 6X 64GB
Xiaomi Redmi Note 4 is best phone in its price range. I am using this phone and it has excellent performance and battery backup. Cameras are also better than my friend's Smartron Srt.Phone . Moreover, MiUi is more clean and smooth and has lots of features. Smartron Srt.Phone 64GB vs Xiaomi Redmi Note 4
srt.phone has a processor miles ahead, quick charge 2.0 which easily compensates for the smaller battery size (which also delivers a whole day of battery life), has NFC and USB-C for future proofing the device. srt.phone can also shoot 4K, which is a big bonus in the 10,000 segment