Select two GPUs from the list there (checkboxes). It will take you to the comparison page where there are two search boxes to type in the GPU you want to compare. It'll show price (usually decently accurate) as well as performance comparison.
On the AMD side you have the 5700xt as the top one at ~$430 (once you select it the website lets you quickly move between the products in the line - 5600, 700, 700xt). I think they have a newly released 5500/xt which along with the 5600 are probably good value.
On the Nvidia side you have the 2060[ti, super] and 2070[ti, maybe a super variant too?].
Never forget, nvidia is very evil :) I didn't even consider buying nvidia for that reason so I bought a Sapphire Nitro+ 5700xt* in November. Had to RMA the first card due to hardware issues but the replacement works great in Windows and Linux. It had driver issues but those have been resolved for a while. I think OpenCL support is still not great in Linux (and maybe Windows) but I don't use that so I can't tell you more about it.
* Nitro+ has factory overclock and upgraded cooler which is silent when not gaming and cool and relatively quiet when gaming. Sapphire generally considered the best AMD card maker; their Pulse and Nitro+ are competitively priced with other variants.