There are three main differences between the three versions.

The firstis the transformation that you obtain. You will gain the ability to become either aqua, wood, or fire elemental depending on your version. Each has their own advantages and disadvantages.

The second difference is the giga cards that are exclusive to each version. There are fifteen total, five in each version. These cannot be traded to the other versions.

The third is what bonuses you give as a brother. For example, someone with leo version would give different stat boosts as a brother than someone with dragon version.

I hope this helps. If you are unsure of what any of these things mean, or if I didn't explain it well, it is true that there are forums for these specific games.