The Game Time + Training package is extremely popular for X-Men decks, and for good reason. Every single Training card is already playable on it's own, so Game Time at a minimum turns 1 resource into 2 ATK or THW, and usually 3 ATK or THW. A fantastic rate, and at a cost of 1 card can almost always be packed into a fully efficient turn. You might have to wait a turn or two before you can keep an ally in play and attach a training to it, especially since each aspect only has access to one, but once you do it's off the races. Very powerful and worth building around as the core strategy of your entire deck.

Quick reminder for those building their decks: all 4 "Training" upgrades applicable on allies can only be played on allies with the "X-Men" trait. The only other training card is a Psyloche hero exclusive.