I had some experience with a cheaper car, and I can see the pros of both options. A new Solaris is all about predictability: warranty, no hidden problems, clear service history. It's comfortable for city driving, parts are cheap and easy to find everywhere, and the service center won't rip you off. The downsides are obvious: pretty basic interior, not very dynamic, looks like an economy car.
A BMW 3 Series looks way more elegant and is more fun to drive, but reliability is a whole different story. Even if the car's been serviced, you never know how it was treated before. German electronics love to act up, and fixing a real premium car can cost you a fortune - sometimes even a simple part replacement costs as much as a whole month of Solaris maintenance. If you're ready for the day when you need serious repairs and it'll hurt your wallet, then you can take the risk.
For city driving and reliability, I'd still go with a new Solaris. It's a bit boring, but you won't be losing sleep at night thinking about how much a transmission replacement costs. And if you want the premium feel and you're cool with surprises - look for the freshest BMW possible with a full dealer service history, that lowers the risk.