I have a Mercedes C300, owned a CLA 45 AMG, and have driven a Tesla Model S for about 50 miles once. I loved my CLA, but I traded it for a C300 and made money off the deal (CLA AMGs are in hot demand).
The CLA 45 had a great engine but suffered from a conservative transmission shifting algorithm. Sport mode was fine but comfort mode was designed for "A to B" driving at low fuel consumption. It also has responsiveness problems from full stop - this wasn't turbo lag per se, as if you don't notice it in launch mode. Once you got going, it was very fast.
The Tesla interior is nearly identical to a Mercedes-Benz interior (they use many of the same parts), with the exception of the large tablet screen on the Tesla. It feels more like the low-end CLA interior than the wood grain C-class which feels more like the S-class. The Model S backseat is cramped compared to the Mercedes, it is more like the BMW 3-Series in terms of leg room. Practically speaking I would go with a Model X.
That said, to me while the throttle response of the Tesla was truly amazing, the regenerative slowdown effect was.. weird. I really didn't like it. Given the price difference between the C-Series and Model S ($55k vs 95k in Canada, and $130k or
More for a model X), I think the C-class will continue to win out except for those with significantly more income. Tesla sells a better car, but not 2x better. Mercedes has time to catch up with its own EV.