This is one of the most concise reviews ever written and it is spot on. I wish I could be like Captain Kirk and own both because I would be just like him, the E90 M3 Sedan and 1M. Unfortunately, after agonzing between the E90 M3, I went with the 1M but I still have a sweet spot and hope once I pay off the 1M to buy a used E90. With that said, I still keep on this thread because many of the problems and components in the M3 are the same in the 1M. The brakes, rear diff and axles, some suspension, mirrors etc. There seems to be some confusion though that the 1M is just a 135i so this review would not be useful to the original poster. While the 1M has the same motor as the early 135i, it has a lightened flywheel, more power and torque including an overboost function. The sheetmetal is bespoke to the 1M. It is not a body kit but actual bulged sheetmetal that fits wider tires. It has a full lock M3 diff where the 135i and 335i have open diffs with some electronic pseudo LSD-like features. The suspension in the 1M is mostly aluminum like the M3 and the brakes are the exact same as the M3 in a lighter car. It comes with M3 competition package wheels and tires (non-runflat) and a new version of the 6 speed gearbox that as Captain Kirk mentioned is really a great feeling gearbox.
So the point is not trying to pump up the 1M in an M3 forum just clarifying that the 1M review will not give you a valid idea of the 135i. It is not as stiff riding as the 1M, it is actually more comfortable and comes with run-flats. Its also quieter than the 1M.
With this said, here are my two cents for the poster. If you can afford the M3 with an amazing normally aspirated V8, it is a car you will tell your kids about in 20 years. However, having an enourmous financial anchor around your neck both with payments and gas bills will take a lot of the fun away. The 135i and 335i will are bitchin' cars and you might enjoy them more if you have some extra money friday night to go out riding to a nice dinner.
Around town, the turbo motors are pretty fun and are no slouches. Good luck.