what is the best banner you could pull from this year?

Define "best". The greatest chances of getting a rate-up servant? Best rate-up servants available? It comes down to which servants you want. Purely from a gameplay perspective, Merlin is largely considered the most broken servant in the game, meaning if you want the best chance to make the game easier, save everything and roll on his rate-up banner at the end of the year.

Though if you ask around, most people will just tell you to roll for the servants you want and ignore their in-game value. The game does not require you to have the best servants to beat it. If you like Martha, then roll for her. In case you didn't know, you can use the Japanese server's banner list to see which servants are on rate-up in the future. Pick a few you like and save for them.

Personally my strategy was to save all my quartz for 2 servants this year (Jalter + Merlin) and roll tickets for everything else. It's worked out alright so far, but my experience isn't likely to be the same as yours.

I’m putting. Everything. I have. On Merlin. I don’t buy quartz very often due to financial obligations but I intend to drop enough to get him in particular. As for the others? We’ll see.