While I wouldn't call it useless, I agree that it's not very helpful with the game in its current form. I'm sure there will be content later down the road to make them shine - maybe even a dungeon designed around companions - but for the moment it seems to be a gimmick at best.
As for choosing a role, I think the safest bet would be the offensive skill line. As Ramiren pointed out the tank role doesn't appear to be very reliable. You can probably make it work by letting your chocobo build some hate first, but it seems very situational.
Healing might be useful to some degree, but their potency and intervals between cures seems rather low. However, keep in mind that skills get more expensive further down the line. The last attack skill costs 10SP - enough buy the first 4 healing skills for example. So I'll probably end up with a combination of healing and attack to get the most out of my points.
