I see most people prefer the Concussion Missiles, I know it is almost a guaranteed one damage but maxes out at 4 damage. Cluster Missiles can peak at 6 damage. They are the same points and both require a TL so why do most prefer one over the other?

I don't know about anybody else but I prefer them because of the blank to hit, and 4 dice to start with, plus with guidance chip being only once per round concussion missiles has better hit chance that two sets of 3 dice attacks, this kinda assumes you launch them using your target lock and also having a focus, (though rage and other EPTs skew this)

Assuming we're talking about a generic ship firing these things, Concussion missile expected damage is 3.5 with no modifiers vs 0 agility, with only guidance chips modifying the dice. Cluster comes in at 3.9 - so far so good for your point.

But then you have to factor in that clusters deliver their damage across two attacks, averaging 2.4 and 1.5 damage each (the higher number represents the attack you choose to use the chips on). Against a ship with decent defence - i.e. 3 agility, you're trading +.4 expected damage for an extra 3 agility dice being thrown against you.

Tldr: Concussion gives better spike damage, and is therefore more threatening to aces in particular.

Clusters do tend to be better against lower agility ships. And when you have modifications that work for both attacks, taking clusters makes sense as well to take advantage of that. Also you need to think about targets having tokens and getting them to spend those tokens and then taking another shot can also be advantageous. Personally I like the idea of clusters on Redline who gets to reroll both attacks, Boba if he's in range one of something to reroll attacks and him or any scum ship with glitterstim that gets unlimited focus for both those attacks. Other reasons can be for just performing two attacks to get other things to trigger like Cracken giving two free actions when he fires clusters. So they have their place, but of course a 4 dice modified attack will have a better chance meeting its mark in standard situations.

Personally, Cluster Missiles allow a possible take down of several ships. One of the first matches I had where my Z-95s had the cluster missiles was against a tricked out Carnor Jax. Bad rolls for the Imp player resulted in his Jax eating one damage from the first strike and two from the second.

That being said, anything that can help you maximize the damage with them will help out. In addition, with the new Guidance chips being a 0-point modification, it frees up points that can be used to either get better pilots or better gear for the squadron.

Personally, Cluster Missiles allow a possible take down of several ships. One of the first matches I had where my Z-95s had the cluster missiles was against a tricked out Carnor Jax. Bad rolls for the Imp player resulted in his Jax eating one damage from the first strike and two from the second.

Average rolls with a tricked out Carnor Jax ( focus+evade with Stealth Device) against average rolls with Cluster Missiles with only Guidance Chips is probably going to result in no damage being done while Concussion Missiles still have a reasonable expectation of being able to push some damage through.

The other advantage that Concussion Missiles have is that they are usable at range 2-3 instead of range 1-2. Having an attack that can negate the bonus defense die from range can be golden.

If you are expecting to encounter a lot of 0 and 1 agility targets Cluster Missiles are great. If you are expecting to be shooting at a lot of 3+ agility targets then Concussions should be better. I'd guess that 2 agility targets are probably close to a break even (though I haven't mathed it out to be certain).

If you can get mods on both attacks with the Cluster Missiles (e.g. with N'Dru + Lone Wolf + Glitterstim), I'd go with them. In all other circumstances I'd take Concussion + Guidance Chips because they have a better chance of doing more damage without extra modifications (excluding the chips) and a better chance of punching through high agility ships.

What about Krassis Trelix?

Im thinking on fielding him with Cluster Missiles + guidance Chips.

or would he be better off with Concussion missiles instead?

he gets a reroll on both attacks and can mod 1 die from 1 attack, i'd go clusters