Welcome and good luck to your wallet as the bricks will hunt down every single $ in there and there will be no end to it! Infact, it will get more addictives the longer time you are in it! 

For your question, most of my collections (let say about 70%?) are vehicles/cars related and its from various themes (eg: Racers / Creator / Speed Champions / Technic / etc)

I am quite sure we have other taikos here who collect everything!   

I mainly focus on Superheroes cause I like Lego's take on the superheroes and their villain. Lately i am branching out abit to City (they need more space theme and aircraft theme) and might dive into Lego technic.

Just completed my whole set of SHELL seasonal collection except the tanker, i think that's it for my collection this year.  Made a SHELL Ferrari racing Pit stop. 
Photos:

wait till u already married then u know..lol..luckily my wife approved lego

Better get her approval bro. I bought a guitar senyap2 and once she found out, I never dared to do it again.

Her argument: Why didn't you tell me? You know I won't scold you. I support you.

So from then onwards I tell her I like this Lego, etc. She approves and helps.

But I know my limits (budget and available cash) thus she approves and I don't use advance money (cards)

All the best in your marriage bro! Welcome to the club!

CONGRATS !   
But dont beli senyap2 ...
Later find out more worst   
Yeah ! totally agreed 

Yes, bro. 
this is TRU KLCC   

Awesome set! I really like the end product especially the working steering features. Simple building technique but it works like a charm