Based on the dev blog, the game is going to be using the 616 universe colors for the infinity gems.
As you can see, the power gem is red in the 616 universe unlike where it is purple in the movies.
What color did the gem example show?
The red page is labeled power gem.
Also, the power gem page has a muscular arm for its infinite node. The Dev Blog already stated that the infinite node is the one that grants attributes.
it offers five distinct investment choices. One of which raises an Attribute and has an infinite maximum!
Based off this, I'm assuming the power gem gives strength. What else could an arm represent in the attributes?
There are six infinity gems and six attributes in the game.
Based off of all this information, I made an edit on MS Paint.
P.S: I put fighting in center because it's confirmed to be the universal stat*, but Speed makes more sense going into the Time Gem.
*everyone benefits from it although the appropriate heroes benefit more
While Fighting will still be the baseline best for pure offense, characters like The Hulk should probably itemize for Durability and Strength since he will get much more damage as a result, which makes the most sense for the character.