The RTX 2070 is better than the Vega 64
on paper, as it sacrifices a tiny bit of things that are already done above exceptionally well to boost some weaker aspects to make for an all around better card. However, as it's pretty much brand new, it's bound to not have too good compatibility right away until the drivers are at a point where they have sufficient compatibility with games and other GPU heavy programs (eg: drivers for brand new cards are often badly optimized). In the long run (I'd say from the third month and on after release, currently at one), the 2070 is much more worth the money around that range.
Just to make it easy for you, use that website I keep linking to to compare the different parts you are interested in. For GPUs, it's important to note that in the "peak bench" section which is what you should be looking at, many cards will be strong in some of the benches with considerably lower performance in others, while other cards sacrifice a bit of what their equivalent cards are good at to boost the weaker one. For example, in the comparison I linked above, the Vega 64 is a fair bit underwhelming when it comes to MShaders (which controls shadows, reflections, collisions, etc. in games and fairly important in parallel processing GPU programs) getting only 191FPS in the benchmark, while the 2070 sacrifices a bit of the other benchmarks to hugely boost that weakness and give an all around 249 minimum FPS. Basically, see whether the card is strong for what you want it for and pick one that's good at what you want it to do. Also, if you don't want shadows, reflections or water effects at ultra settings, then the Vega 64 will instead give you a slightly better performance. In current games though, both run everything at ultra without any issues at a minimum of 60FPS.
