RTX is newer and faster.

GTX 1080 and RTX 2070 are equivalent in speed.

https://gpu.userbenchmark.com/Compare/Nvidia-RTX-2070-vs-Nvidia-GTX-1080/4029vs3603

Why would NVIDIA make 2 separate graphic cards? what are the pros and cons of each one? 

In a nutshell, RTX has ray tracing and DLSS support.  Google is your friend here.

GTX stands for Giga Texel Shader eXtreme and RTX stands for Ray Tracing Texel eXtreme, these are not a simple technology to understand by any means but the most basic difference between the two is that the RTX is specifically designed for performing Real-Time Ray Tracing.

You may read more here to get better knowledge about gtx vs rtx, then you'll get ideas about what will be better for you.