I'm honestly not sure what I would do if my E90 got totalled tomorrow. I guess I would search for another low option E90 but I would probably end up ordering an F80. I don't see any downside, just a different car. Wish nav wasn't standard but oh well. Each M3 has had a distinctly different character and this one is no different. M cars aren't like the 911 or vette which have been literally the same formula for half a century, each iteration has its very different characteristics from the last with the possible exception of e28-e34 and e36-e46, but even there you have a hugely more modern chassis replacing the outgoing model and on a much shorter life cycle than the vettes and most gens of 911.
Each M3 has been lovable for its own reasons and this one will be no different. Collect them all I say
As for m4 vs m3, the coupe has always been an aesthetic choice for peacocks or big people who need wide door openings, so picking the sedan not only nets you the correct car but now also the correct badge. Win
For me the M3 has no competition. Smallish 4dr sedan, RWD, fast, manual. That is a class of one as of this writing, sadly