If you're not using FP for drafts, then I can see one of two ways to quickly get fifa 17 coins free using the coin boosts.
Beginner TOTW will be quickest way to use the boosts, as you can play 4 matches per hour by just keeping the ball where the defenders won't tackle you. In my experience on FIFA 16, you get around 400 coins per match, so with coin boosts it's ~1.4k per match which means about 56k during the 10 hour trial.
Do we know what the offline season rewards are? If it's the same at FUT 16, and assuming a slightly longer time at 20 mins per match as the difficulty is higher, it should be a maximum of 56.3k including coin boosts. You'll need to win every game to get this rate, except you can draw a single game in division 8 and still win the league there. This includes winning 18 matches on world class difficulty, and two on legendary. You'll also get some pack rewards; on FUT 16 it was a bronze, a premium bronze and a silver pack from divisions 8, 7 and 6.
So if you're good at beating the CPU then seasons is a slightly better choice. It gets much better if you're planning on using another EA sub to add another 10 hours to your trial, as you'll reach higher divisions with higher rewards. But if you can't reliably beat the CPU teams on World Class difficulty and above, then playing TOTW matches is the best way to gather coins.
Bear in mind though that it's possible that with the new game modes there has been a rebalancing of offline seasons. I looked at FUT 15 and the rewards were pretty much the same - only D10 and D9 were increased by 100 coins each. Even if it does change, we can just re-evaluate when the trial does get released.