Hi, I've seen a lot of people building just infantry for defense.. Is this the best defense chassis or are they all equal and just a matter of preference? :s

every chases have advantages and disadvantages... so I don't think Infantry is the only thing best for this

Just to be clear from a recruiting standpoint (unless you take into account building the structures to unlock them) every chassis costs the same.

and if some 1 don't know, by "costing same" means as 1 tank=3 Infantry so 1 Armour Tank will cost same as 3 Infantry armour units i.e 300 metal ( 1 armour tank):300 metal (3 armour Infantry) ... in start, without Over-head

and 1 Vehicle = 2 Infantry
so its 3 units inf= 2 units Vehicles=1 Unit Tank

That's a complicated and wordy way to say it, a simpler method would be no matter what the chassis is it will cost the same to build a full squad.

this does not answer the guys question. actually best defence is the shield of 12 ticks... but speaking of chasis of units it depends on your possible enemies atack. and considering that your enemies chasis is infantery - lets say- you build the next gen of weapon and if you just defend make them all armour. you save resources and you got the best defence

No, just armor is a terrible defense. It is extremely easy to take down full armor squads and the enemy units still get xp.

Armour is good for defending ranged units , which attack first.
Also there much more easy to replace.

Given the context of the question armor would not be the way to go though since he is talking about defending a colony.