Where and when do you buy your tickets?

I haven't seen this asked in a while, and a search brings up results from two years ago, so let's see.

I'm going to the game on Saturday, and it should be a popular one considering the giveaway. I notice tickets are far cheaper through a third party than with the Mets directly, my question is, will they continue to become cheaper? Should I buy them ASAP or wait until Friday or even Saturday?

What about just in general, if it was a weekday game?

Thanks everyone