Hypothetical Situation:

Assume your enemy (1 colony, its 1 vs 1) is building Range Soldier Squads (10-20) and Range Vehicle Squads (5-10), which would be the best load out to counter him with?

I have built Range Soldiers (lazer, 10-20) to counter the Vehicles but how do I counter the Soldiers? Or is there a better method? Tell me, thanks.

Partly depends on what the enemy is using. But you should try to outnumber him by so much that you win in 1 round to minimise losses. Which is usually about 3x more than he or she has.

So I would make 2 or 3 squads of anti veh and 3 or 4 squads of anti inf (concussive).

best bet would be inf, since they deals 30% more damage to the vehicles. But they don't deal more damage or receive more damage from enemy's vehicles or inf.

While tanks are considered best against inf, it has disadvantages against vehicles. So it's not a good choice.