Whenever you ask the question about the 4 pot petrol or diesel you will always be pushed towards the 6 pot
I owned a E92 320i N43 petrol for 5 years before it was stolen. I can manage DIY repair to a certain point therefore saved a few ££ during the 5 years. I ended up replacing all 4 injectors and refresh front/rear suspension.
The E90 325i/30i N53 has some weak points like the leaking fuel injectors and HPFP.
I have seen in forum owners pickup a bargain and later cry all 6 injectors need replacing which cost £250+ each plus fitting cost. If you are gonna purchase a old petrol version i suggest purchase from seller that can show evidence of recent injector replacing.
If you are tempted to purchase a N54 335i.... i suggest do some homework and put aside few £k for repairs.
All the best