While you may find "720p" or "1080p" files on unofficial download sites, the most reliable and legal way to access the complete first season in high quality is through official platforms:
The complete season 1-7 (720p top) of Avengers: Earth's Mightiest Heroes is a comprehensive collection of all 52 episodes, plus several bonus features. This collection offers: avengers earth39s mightiest heroes complete season 1720p top
, features a vibrant, "comic book leaping off the page" style that pops with clarity in HD. Vibrant Animation While you may find "720p" or "1080p" files