5G is initializing in two manners - sub-6ghz spectrum and millimeter wave. "Sub 6" deploys on radio towers on which 4G (LTE) is already deployed. AT&T and T-Mobile have most of theirs in the 600mhz to 850mhz range. Verizon has deployed theirs in much higher bandwidths. The advantage of the lower spectrum is distance and penetration through walls and other physical objects. Millimeter wave is deployed in spectrum which is effective over shorter distances without physical obstructions. It's advantage is bandwidth. "Big pipe" offering individual users in public spaces, stadiums, and the like up to 1gb down/up. All providers have deployed both "Sub 6" and "MMW."
5G technology can reduce latency to near zero. This makes possible real time applications (antonymous vehicles, interactive holograms, etc.). Improvements for today's uses include faster downloads, higher definition, and "glitch-free" streaming experience (assuming no problems at the server).
Today, according to independent tests, AT&T's 5G and LTE networks perform best overall. T-Mobile is next for 5G, having similar spectrum. Verizon is playing catch-up.