I think GM deserves to be at the top of the list. Cruise is very quickly closing the gap between themselves and Waymo, and they have a comitted car company to back them up. The jury is still out as to whether Ford can make good headway on their 'secret sauce', which is now in the hands of Argo.ai.
Yeah, Cruise seems to be doing a great job. Argo has a great founding team, but there are still a lot of things that can go wrong. While I'd give Argo the edge in technical competence (I realize that's not a very meaningful statement considering the age of the company), what really matters is building the right product at the right time. You can have a ton of great engineers and still not accomplish much in the market - just look at Waymo and Uber.
The way I see it, at least in the US, it's really GM vs Ford (which is Cruise vs Argo). Waymo has a management crisis and lost most of their top talent, and Uber is hemorrhaging talent (and money). Apart from that there are various startups but I don't believe they'll ever get the money necessary to compete with the big players - even Google gave up on that front.
Outside the US I'm excited to see what happens with Volvo, which says they'll have 100 stage 4 vehicles delivered to customers by the end of the year.