Most people do not realize that Rivian looks very competitive and value on "paper" only. Even Tesla looks good on paper, but there are tons of other things that you need to experience to determine how actually they deliver. Millions of Tesla cars out there now and driven everyday and being praised and criticized. The biggest advantage of Tesla is that they gather tons of actual driving data from the cars on the road every second/minute/hour, etc for continuous improvement and feedback.
I currently have a 2018 Performance Model 3 with FSD, and I'm in the final process of getting a Rivian R1T. I haven't decided yet on whether I'll trade my Tesla in on the Rivian or if I'll trade my Jeep Wrangler Unlimited in on the Rivian.
For me both of them have their strengths and weaknesses.
With Tesla its by far the Supercharging network being really solid, and dependable. I could travel places without much concern about being able to charge. Sure the Range has never gotten anywhere close to the promise 310 miles, but it Superchargers quickly and its not too big of a deal.
The biggest weakness of Tesla is the lack of customer engagement. There are so many things that don't work like they're supposed to, and it can be maddening. For example the automatic lights no longer turn on in the rain during the day like they used to. Now you have to make sure to turn them on manually or you'll be one of those idiots who doesn't use their lights in the rain.
FSD progress has been painfully slow, and even the AP experience isn't at the level where I wish it was. What I want is an ultra smooth AP experience on freeways with minimal phantom braking (no more than one moderate one per 1K miles). What I currently have AP that's barely useable during stop and go because it accelerates too much. It basically launches forwards. It used to be fine in early builds, but it's been pretty bad for awhile now.
Overall I love my Model 3 when I drive it manually, and its okay on the freeway while on AP as long it's not stop and go. The NoA never worked to the level I wanted to due to mapping issues. There is no way to report maps issues where Tesla fixes them.
With Rivian I expect to lose out on things I really like about Tesla like the trip planner, and the navigation is supposedly way worse.
In a lot of ways its going back to how things were with Tesla back in 2015 when I bought a Model S. Sure it didn't have all the features they now have, but it was an exciting time.
As long as Rivian gives me Dash Cam, Sentry Mode equivalent, and auto lane change with their driver+ system I'll be pretty happy.
Most of my decision really comes down to the fact that Rivian is the new shiny thing, and I've wanted a TRUE 4x4 EV for awhile.
Over the last decade or so the roads around me have really deteriorated. So I find myself more relaxed when I drive my Jeep as I can just run things over. I can also see over bushes that they never cut down just to see whether someone is coming when I turn onto a road.
If I keep driving my Model 3 I'll probably get arrested for taking a chain saw after bushes that grew too high to see over them.
If I do trade in my Model 3 what I'll miss the most is curvy Mountain roads.
What I won't miss is the Safety Score. Ugh, that sucked just so bad. So glad I finally got FSD beta so I wouldn't have to do that again. But, FSD Beta never really did much for me. If FSD beta did useful stuff I doubt I'd trade the Tesla in.