Marvel 3rd anniversary event has started.
For the next 2.5 weeks. This doesn't give out big login gifts so much as a bunch of useful benefits. It's probably the best time during the year to try the game.
- XP boost for faster leveling
- "loot explosions" give some of the best gear as well as currencies for endgame
- collect "cake slices" to get things like an extra shared bank and a choose (almost) any hero unlock token.
For new players I'd suggest picking Captain America or Scarlet Witch as your one free unlock since they are both considered strong at endgame. As you play and through events you'll have the chance to unlock other random heroes without paying cash.
Also, donate junk to the Crafter and Enchanter at Avengers Tower instead of selling it. You want to level them up to 10 each, then 20 for the crafter. But you can skip crafting and enchanting until you reach 60, save the mats.
If you have space, it's worth saving "unique" items even after you stop using them. At crafter level 15 he learns a recipe to convert uniques to a lot of credits. If you get a Pet it's also worth feeding them to it instead of donating.