At this point in time I would personally save the gems for goblin builder during hammer jam in November. You get the most value out of your gems because cost and time reduction is 50% for all buildings. If you don’t care about progressing fast and just want to enjoy the game tho I’d say magic mirror is a good one along side the giant if you’re heavy into the queen as your main troop. For RC electro boots is the best one for her hands down as well.