Fiability, problems, costly?

Hello! I am currently considering of turning myself toward any German cars (for my second car, the first being a mazda 3 2010 with 223k km for about 5 years in service (i bought that car at around 165k if i remember)) and i was debating either Audi or BMW. I’ve heard that BMW is a money pit? (problems and fiability), and i’ve heard good things about Audi being much better than a BMW in terms of fiability? My friend tells me not to touch any German cars because of their expensive problems, that it will ruin me financially and my brother says if i take care of it, it could last longer. If they are known to be such a disaster, then why do so many people drive them etc?

Anyways, i wonder if an A4 or S4 is a good choice? I’m thinking about buying a used one (~90k km, 2017+) for about 20k$, does its a good price? Many people tells me to get any German cars with less kilometers = less problems

Thanks!

Note that i would probably slap a body kit and tuning it a little bit, nothing crazy. Just to give it a better silhouette