HGG Community Forums

HaJ1
Game year lasts 2 real-life months
Exceptional breeders and showers are included in the game
Therefore Boost tokens available
More shares available for DHH's
Era 0 horses can be speed trained
More players (although this may have changed by now)

HaJ2
Game year lasts 1 real-life month
No exceptional breeders and showers except for 1, very early Rank Special
Therefore No Boost tokens
Limited number of shares for DHH's
No speed training
Higher percentage of points for weekly showing bonus (to offset lower leveling off points and reduced earnings because of the shorter game year)
Sometimes used as the beta-testing platform for game changes

These are the primary ones that come to my mind this morning.