I'm on the fence myself, but on one hand it's all up to the way that you use the vehicle. I've got both an X LR and a R1T on order. Tesla is currently selling only the 6 seater where the middle row doesn't fold down, meaning that you lose valuable cargo capacity. Although it's got a 5000 pound tow capacity, it can only handle 120 pounds of load downward on it's hitch because of it's design. You cannot add anything to the roof because of the Falcon Wing Doors. This means towing bikes on the back is a risk - which I am planning on doing so with my family of 4. My outstanding order is now 14 months, with another 5 to be delivered even though I was "promised" a 2021 delivery by doing the 6 seater instead of a 7. After a year, Tesla is still ramping up production in starts and fits with middling quality. By that same stance, my R1T isn't going to be here until sometime in 2023 because of the Max Pack config. The latest news from Rivian is disappointing and cause for concern.
If you're planning on taking gear, going off road, I would say the Rivian is the better choice. It's a quick thing to add on the racks since it's designed as such, gear guard, the tunnel, a power operated frunk, working surround camera, air pump are all benefits, and the truck is just plain old utility without compromise. I have little to no fear of chucking something at the Rivian, but would cringe doing the same thing with the Tesla.
Tesla has some advantages - Supercharger network, better software (for the moment) and a bit of history to it. I've not had problems getting my S serviced with really only the rear camera going out within 2 years and no other problems for a total of 5 years now. It's been a solid car. I suspect, however, that the X will be a bit more finicky.
At this point, it might just come down to whoever can deliver first gets the money. In the mean time, I can invest some time into the details and do some soul searching to think about needs vs wants in order to come to a reasonable decision.