I recommend Stubhub. First, Stubhub's pricing is all in. So the price you see includes all the fees. It's almost always cheaper than the prices the team is selling them for. And they don't list all their fees on their prices. Also, Stubhub gives you rewards points. So if you buy enough tickets to any game, you'll eventually earn a discount on later tickets. Buying Padre tickets from the team doesn't help you later to buy Dodger tickets for less.
If you're like me, you're excitedly planning your trip and can't wait to buy your game tickets. Don't be like me. Wait. Go to Stubhub and look at the prices of tickets. As the game gets closer, the price of the tickets goes down. I've been monitoring some games since early February and have seen multiple price drops for my tickets of choice.
This happens because few teams sell out. So the supply of tickets is usually greater than demand. If the game is sold out, there may be a lot of demand.
If you're buying 2 or 4 tickets, you can stick to this. If you're buying only 1 or 5 or more, your selections may be limited. So if you see a decent price for the number of tickets you want, jump on it. The price in that section may drop from $40 a ticket to $30, but it's possible that the only people offering 6 seats together might price them real high.