Yea GPU is definitely the way to go and investing in the new RTX cards is a good idea. I talked to someone over at Puget Systems and they mentioned with renderers like Redshift we can expect 1 RTX 2070 to equal 2~3 GTX 1070 cards as they begin to take advantage of the new technology.
There really isn't an argument against GPU rendering, speeds are hugely faster, that's why Solid Angle is developing it.
The only other thing against GPU rendering is scaling the hardware. It's harder to scale up and network GPU's as they connect through the PCIe slots. Putting together a single system that supports more than 4 cards is pretty challenging at the moment. Render farms generally charge more for GPU rendering probably because of this.
For most freelancers working on a single system though, GPU rendering is really the most practical.
