Posting is a good way to earn gold~ You just need to find a thread with really friendly people to talk to! You'd also be making more friends and become closer to the community~ :)
Technically, the fastest way is to donate and then sell the hearts for gold.
I would then say art, if you're fast enough and really great you can make a significant amount of gold selling your arts (especially with auctions) It might seem like it takes a bit longer, but the fact is that if you make 250k from 1 auction, it's likely going to make more than posting for the same amount of time.
Exchanging, you need gold to start but if you know what you're doing you can really make a lot of gold. This requires a lot more skill than anything else.
Posting - If you find a good active forum and get in a squad you can do some serious damage to your goal, make a lot of gold quickly. Once you make gold you can do some exchanging to make more gold if you're willing to take the risk.
Games @ 750g a day can be helpful
Events - getting spare items and currencies to sell in the exchange.
Marbles, might not seem like a lot but you can get gold or items to sell.
Games is actually faster to me. I can get the max 750g from pegs in about 10 minutes. But I'm not much of a poster so that's why games work better for me. I really think it just depends on what you like to do in general.
The best thing ever is when you get into a couple chat threads that are moving at a decent rate and just have a good time talking to people. An hour later, you just feel like you had a great time with funny people and then you look at your gold count and whoa.
The fastest way to earn gold would be posting.
I just joined about like 2 hours ago and I already got a few items.
Plus I got 375 gold left over, I know it's not much but it's something for a newb.
Hopefully I will find places to have good conversations, so my avatar can look even better.