People may think I am crazy, but I upgraded from a Model S P100D to a Model 3. My prior car before the P100D was a P85DL. It all started when my wife traded in her Model X for a P3D. After driving my wife's 3 for some time I decided to sell my P100D and buy another P3D (different color of course.) I have been in a S since 2014, and there are certain things I think are markedly improved in the 3. I know that there have been a lot of quality issues, especially early on, but I find the quality overall improved, and for the longterm I think it will hold up better.
Things that I think are better improvements are:
-Performance- I think the 3 handles much better, and with performance brakes, brakes better. The S was more of a straight line shooter, the 3 is a much more all around package. I envision it kind of like the feeling of an M3 versus M5. You could really feel the weight of the S in the corner at the limits, even though it hid it well, it always telegraphed a desire to understeer at the limit. The fact that they moved both motors of the 3 to the center, inside the axels and thereby lowered the moment of polar inertia is staggering brilliant. They essentially created almost a mid engined car feel in a car with instant torque. The car surprises in the corner with it's willingness to turn.
-A/C I think the AC is way improved,
- Screen is markedly better and higher resolution. (I had to keep having my Model S screens replaced because of the delamination issue of the adhesive causing the yellow around the edge.)
- Doors are improved. In the 3 they close solidly, in both my Ses they always seems a little "off" kind of double hitting when closed.
-Seats - I think the new Tesla designed synthetic seats will hold up better, and to me are more comfortable
-Stereo - I had the upgraded stereo in all our prior Teslas and I think the 3s is hands down better
Headlights - There is no adaptive lighting, but overall the 3's headlights provide better illumination
Efficiency / cooling - Even In the performance version and with a heavy foot the 3 with two different motors (3 phase AC induction motor, and permanent magnet motors) in tandem are much more efficient. Using innovations that are not in the S or X, or any other EV for that matter to increase the efficiency such as simply arranging the batteries in a Hallback array is amazing. I also don't see as much a hit driving in cold weather. I also am glad they improved the cooling of the batteries by having a higher coolant loop to battery ratio. I am also looking forward to the ability of the 2170 battery cells to be able to take advantage of the faster charging rate of supercharging 3.
To each his own, but I think it would be a bad time to buy an S or an X with the reported update refresh coming. I remember when autopilot 2 was just coming out, everyone said no one would want it, and everyone would prefer autopilot one when trying to sell it. I can tell you that isn't the case, in trying to sell a used Tesla everyone made sure the cars had autopilot 2. In the same way I think that when the S and X get refreshed with newer, more efficient battery cells, improved motors, better AC, and headlights, current versions may take a value hit. Just my 2 cents.
I would be happy to answer any specific questions, and realize they are just my own opinion.