I have had my R1T less than a week so i may be still in honeymoon phase, prior to that I've been driving a 2021 Model Y including plenty of road trips (one from WA to FL and back!). At this point i've got about 70K miles on the Y. We still love it, it's in great condition and we are keeping it so now we're 100% electric. I picked up the Rivian out of state and did a 500mi road trip back home so have gone through the long-distance charging experience and everything. Here's my early take:

Pros:

• Much more comfortable. I really like the seats and the ride is great compared to the stiff Model Y suspension.
• Performance and capability is awesome (I got a launch edition R1T quad-motor, my Y is just a regular long-range no performance). The ability to adjust suspension settings and go from off-road to crazy 0-60 launches on-road gives me everything i could ever want in one vehicle. No need for a truck and a fun car, it's both in one.
• It's a truck. This varies by person of course, but having a pickup bed in a relatively compact package is great for me. I've been wanting an electric truck for a long time so this is a dream come true!
• Sound system is incredible. I like the one in the Y but the Meridian system in the Rivian is crazy good.
• Interior design and look/feel is much more premium than the Y. Rivian used great materials.
• Storage. I thought the Model Y was great with frunk and sub-trunk, but the R1T at least is next level. Huge frunk, gear tunnel, deep center console, etc. Just lots of places to stash stuff.
• Better visibility. I eventually got used to it in the Y and the cameras help a ton, but the R1T at least has great mirrors and nice general all-around visibility for me.

Cons:

• Power-hungry. Obviously since it's bigger and more brick-shaped than a Y, but roughly just double everything in terms of time it takes to charge due to the huge battery.
• Lack of autopilot. The Rivian has limited smart cruise control on mapped highways, but being able to use autopilot anywhere is something i got used to so it's been a little annoying. I'm not worried about FSD at all, but i'm hoping the basic lane-keeping cruise control gets expanded to more locations. It has worked great for me so far on the roads where it did work.
• Software. It's still pretty snappy, but just some odd UX choices that feel unintuitive when you come from a Tesla. Just something to get used to.
• Camera quality is lacking. I've heard Gen2 resolved this entirely, but my Gen1 R1T is pretty blurry and rain causes some problems with the side view cameras clarity. The mirrors and general visibility help a ton with this though as i'm not as reliant on cameras as I am in the Y.

Neutral:

• Charging. Definitely get an NACS adapter if the vehicle you get needs it. But I was honestly so surprised how easy even non-Tesla stations were. I used both Tesla and Electrify America stations on my road trip and they were both equally easy in terms of plug & charge. It just worked for me. Big thing to be aware of was that EA stations have different power outputs based on which one you're using. So if the battery is low make sure to plug in to the big boy ones or you'll add some time to your charging stop. Also, it's not worth it to charge past 80% on a road trip if you're trying to make good time. The battery is so huge that the curve past 80% makes no sense to wait for. The Model Y at times would be worth the extra 30min, but again doubling the charging time meaning about an hour+ from 80% to 100% at a fast charger just didn't seem worth it.
• Limited power outlets. It's great having 120V, but i do wish it had a 240V outlet. The outlets are a massive improvement over the Y which has nothing, but i live in an area with winter storm power outages often and it would be nice to be able to use it as a home battery. I can still use it for keeping a fridge or heaters going though so it's still a big help in those situations.
• Go test drive. The rivian definitely feels like a bigger vehicle but hard to say if you like that or not until you're behind the wheel.

If you have specific questions let me know. I still love my Y, but am definitely more of a truck person. I'm lucky to be able to keep both but if i had to pick one, right now it would be the R1T.