Well it certainly depends on what you're best at or what you like doing most, as GB offers plenty of ways to earn points. Obvious one being submitting actual quality content!
Here is a table with (mostly) all the ways to earn points in the site, including how many points you receive from each:
1. Submissions: The most obvious one, submitting just about anything that has to do with skins, sounds, maps, etc... will lend you +25 points, so if you're passionate and dedicated to it, you can essentially amass a good fortune. (Keep in mind that the total points you earn may also vary on what type of submission you make, for example submitting an App will give you +50 points instead of 25.) There is however a little bit more to it: 1.2. Featured submission(s): If your submission gets enough likes, or manages to impress the community at a point where it can get put on the featured submissions window at the homepage, you will receive an additional +50 points. Mind you, it's not going to be quite as easy, unless you're a submission wizard! 1.3. Getting "Thanked": Some users may do more than just liking your submissions, you may upload something they were looking for, or maybe something it's just really pleasing to them... If that's the case, they can "Thank" you, which will donate you +10 points directly from one of your submissions!
2. Logins and Perks: Whenever you login every 24 hours, you will receive +1 point all the time, but there are several "Perks" that work quite like "achievements" which can boost this and help you earn more per login: 2.1. X year member: Members that have been on this site long enough will gradually get higher/rarer perks which will increase their amount of login points based on the respective account age, for example if your account has a total of 2 years then you will start getting +2 points per login. Not only that, but they can essentially stack on top of another, so for instance if you've been here 6 years, the daily login, 1 month, 6 months,1 year, 2 years, 4 years and 6 years will stack up, meaning that for every login you will get +16 points!
3. Community and posts: Luckily if you aren't the most creative, there are plenty of ways to earn points by being inclusive to the community and overall being a great and helpful person. 3.1. Exemplary posts/awards: This is easily one of the most tempting ones and the one that I think it's the nicest. An exemplary post is given to those posts on a forum thread or even submissions that are... well... exemplary! If it gives detailed and very helpful feedback, or it answers a question or helps someone in the best way possible, it'll be awarded as exemplary and will grant you your first "Exemplary Post" perk, which from now on will grant you +1 point for every post you make on a submission (It does not work when you post on someone's profile, keep that in mind). Depending on how many exemplary posts you have made, it can also "level up", giving you an extra point for every post, thus making it +2 per post... +3 per post... etc... 3.2. Bounty hunts: From time to time someone may be in need of something that they lack the skill or time for, so they put up what's known as "Requests". These requests can vary a lot, but all of them have a bounty system which will reward you with the points that have been set by the requester or even some other users that may want to make it more worthwhile. I believe the minimum amount you can get from a bounty is +20 points, however if the request is particularly messy, the bounty may be higher than that, meaning that if you can find a well-payed bounty you may end up getting a lot at once if you are willing to sacrifice your time filling up requests (There are bounties that end up reaching +5.000 points, believe it or not)! 3.3. Donations: This possibly doesn't need too much of an explanation, if a friend is nice enough or if someone has a particularly nice day, they can donate to you through the profile module, any amount with any message. Pretty much anyone knows how it works. 3.4. Subscribers: If someone is fond of your works or really loves to stalk you around as you post stuff, if they subscribe to you it'll give you +25 points per subscriber. It may sound nice at first but personally, I don't think many people bother subscribing unless you know how to target an audience.
I believe those are all the ways to earn points in the site, as far as I've seen from all the time I spent here. (If someone knows of extra ways that I haven't mentioned, add them as a reply or something else.)
When it comes to picking the best, well again, it really depends on what you like doing most since doing something that bores you or makes you tired quickly may stray you off earning those pesky points. If you have a passion for submitting content, I'd say that's personally the quickest and best way to earn points. Otherwise being helpful and writing long walls of text detailing everything praying that the Banana gods give you an exemplary award may also be fruitful in the long run~ Or you can just do many things at once and make the most out of the system.