They're very, very different cars in everything from design to purpose, so I am not going to compare the two fully as it would take pages upon pages. However, as some of you know/can tell, I spend a lot of time around BMW's, but I have driven quite a number of MC's and even raced one for three events.
The 135i is a heavier car than you would think, but it is still 300lb lighter than the 335i. The N54 is a great engine, and it will make more power for less money than the N55, and with the money you save buying a slightly older MY, equipped with an N54, you can upgrade the "trouble" parts with any one of a number of extremely strong aftermarket ones, although I would not buy any car that hadn't had every single recall/TSB attended to and the documentation to prove it.
From the N54 cars I've dyno'd, every single one STOCK shows that BMW vastly underspecced the power output, with 300 REAR WHEEL HP and over 300rwtq being fairly common.
I would recommend anyone who enjoys driving the car properly set aside money for the following, if you want the engine to last...
- Upgraded oil cooler and possibly transmission cooler
- Upgraded intercooler and New hosing
The two most fun upgrades overall (ignoring my usual "don't touch a darn thing until you have the entire suspension and brakes perfectly setup!" rule of building a Bimmer)...
- Combination of intake, downpipe, and tuner (AFE CAI, Cobb catless, and Cobb tuner), good for a solid 370-410rwhp and if bought as a package, less than two grand while not taking a single bit of life off the engine
- Quaife or OS Giken limited slip differential in a ratio appropriate to your needs; I swear, the entire car changes its personality with the addition of an LSD, making it possible to utilize the entirety of your power band effectively, and properly get on the throttle in a corner
The Mini is a fun, tossable, and very efficient car. I am 6'3" and I find it comfortable with headroom to spare. The greenhouse offers excellent visibility, and the car is extremely predictable and communicative.
I wouldnnever recommend a non S, the base doesn't have any advantage and loses a lot of power.
I am very much NOT a fan of FWD (or AWD), but the Cooper S 6mt is one of the few ever made that I absolutely enjoy and don't even notice that it is driven by the wrong wheels.
Regardless, with these cars, I am going to say now that if you are not willing to be extremely proactive about maintenance, above and beyond anything recommended by BMW, then you should look elsewhere.
There are points in the cars life where you will spend thousands to replace parts that haven't failed, but do it regardless of how you feel on the issue, and honestly, get upgraded aaftermarket parts whenever available as many of them are either permanent, one time replacements, and/or they have lifetime warranties that are actually upheld without a single issue.
Budget $2500 a year for maintenance, most years you won't utilize anywhere close to it, but you should not ever be in the position where you go "I can hold off on that a bit longer", because repairing is going to cost you a fair bit more.
I would spend at least a month before buying a German car, you need to know the issues known and the prevention measures.
FWIW, a modern Mercedes is not only more expensive to operate, they break and they do it spectacularly.
