I have been doing the same If I don't go with a Tesla my next choice is the S3. Should look at the BMW 340XI also. Thinking the Audi A3/A4 and BMW 3 series are the big competitors to the Tesla 3.
I drove a very nicely appointed S3, really enjoyed it, then immediately after made the mistake of taking out an S5 Sportback (not realizing what the sticker was on it - $69k) and that kind of blew the S3 away, which spoiled it for me...
A couple days later I drove an S4 and loved it. In addition to the performance, it has the same luxurious feel as the S5, just minus the hatchback (and much easier to negotiate, because the S5 Sportback are relatively rare and in demand).
For $$ sake, I think I need to go back and give the S3 another shot, having cleared my head of the S5 Sportback experience. Also, for the first test drive, I had my 6'5" husband, my daughter, AND the salesman all crammed in that little thing... which is really not the kind of passenger load it's designed for (or would normally be carrying, as far as how I'd use it).
My sales guy is really, really trying to get me to consider a fully loaded A4 he has, and I'm sure it's awesome, but it won't be nearly as fun to drive as the S4 (or S3, or Model 3, or 340/440).
I have truly loved my 335i (RWD). If not for the new tech that has come out recently (Apple CarPlay) I would probably buy it. My only hesitation with its successor, the 340, is that the 3 series is so common (although 335/340 less so) - it would be fun to have something a little different, like the 4 series, if I go with another BMW.
Anyhow... I fully agree, these are some of the major competitors for the Model 3. I will be very curious to see what comes of the Model 3 Performance version.