I purchased the RTX 3070 to tide me over until I could get a 3080. Despite being a lower spec, it's an incredibly powerful card and would hold its own in most modern systems, playing games at top specs.
If you're building a mid to high end PC the 3070 will be a perfect choice, but if you're going for top specs, opt for the 3080. (Don't consider the 3090 unless you already specifically know the reason you need it; and no, more FPS in a game isn't that reason.)