Play what you most enjoy, are most comfortable with and will prove the most profitable for you......only you can really answer that.
Also 20/30 buyins would be more of a agressive/ok brm for cash tables, I'd suggest 50-100 (i'd lean closer to 100, but single tabling 50 should be decent) for sng's up to perhaps the 180 man's and 150-200 for any fields larger.
The game you play will not necesarily determine your br improvement.......technically i could suggest playing the sunday million if your just looking for the score that will boost your br the most.....but it comes down to skills, ability to improve your game (don't focus on bankroll, that will come with improving your game plain and simple), and solid brm to ensure that if you are a winning player you will not go bust during the ups and downs of varience and have a cushion to improve when moving to new levels.
If you going to play 3.30$ 45 or 180 mans, I'd suggest you have a min 200$ br. You currently have 28$ so find whatever the abs lowest limit on the site is and play it until you see a stead increase in your br over a significant sample (for 9man stt's, talking 500-1000 games to start).
What site do you play? If you play stars and like the 45 man games then grind the 25c 45 mans until you have a 50$ br and then move into the 50c 45mans and so on and so forth. Good Luck