Should i play 3|2, 3|0, or 5|0 blitz?

rn i am playing 3|0.

Also should i play rapid more?

You should play 15|10 and analyze every game if you want to improve

i don't have that much time for 15|10.

I also dont have premium, so i only can analyze once per day.

It all depends on the player. Personally, I prefer 3 minute games with no bonus or anything. (3|0) Longer games might help you learn how to play chess, & help with tactics and mechanics. But short games help gain quick thinking. If you're playing blitz, it all depends on the player & their playstyle. I would suggest playing a few games of each & decide which one you like best.

I like 30/0, its slow enough to be proper chess but doesn't take all day.

I'm not a big fan of increments as its harder to put time pressure on.

Which could also be the positive side of increment because it requires more of the players' ability to win the game on the board...
I hardly play 5 | 0 (and only ever unrated) but I feel that it feels significantly longer than 3 | 0. A friend of mine did say it is much better for improvement. (Btw, he is 2100 blitz and plays blitz primarily.)
I don't think it's impossible to improve with blitz (I've known people who have improved playing pretty much all blitz) but I do think rapid helps more. I hardly play 15 | 10, but I think that looking through a game with the analysis board is very helpful (you don't need a membership for that, just click on Analysis after the game.)