What guys do you think excel at that sort of thing? Who do you think is better, Mak or Loku?

Both are close to useless in my opinion. There is better options for the same amount of points.

The day if the sniper is coming. He assassins with range 7 shots. Overdrive to give them an extra action if you really need it, hunter protocol to surge the meat bags as well as explosive armaments to blast 2 from far, far away. In mos eisely I can snipe you from my deployment zone almost.

Imperial Assault Skirmish is a game of close and personal combat, usually around mission objectives and terminals. Snipers don't fit in too well here.

Ignoring figures for line of sight is necessary for a sniper to be useful at all.

Additional abilities would be necessary to make a sniper shine. E.g.: If there was a way to make use of Critical Hit more often, then Mak would be OK.

Loku's Command Card is good, when he's with Leia. (Use the Command Card, shoot with Loku, shoot with Leia, Leia takes the card back from the discard pile. / Same as Gideon's Take it down.)

Ignoring figures for line of sight is necessary for a sniper to be useful at all.

This. I'm playing multiple campaigns, and each campaign has a Mak player. One person never considered shooting through people, the other one does it all the time and is real effective.

HK Assassin Droids are the snipers you are looking for.

I agree HK Assassin Droids are very sniper-ish, especially the elites with Priority Target.

I think Loku might be decent in skirmish if you can get his Special Forces Focus started, it's easier to sustain it. Maybe not Tier 1 with 4x4 & Rebel Blast, but probably good enough for Tier 2.

The issue DerBaer pointed out is true too. It also manifests itself in the Skirmish rules which mostly limit figures to 1 move and 1 attack. Since you have 2 actions you might as well be moving in close then attacking if you want to hit. If figures had other good things to do with their actions besides move, of if you got move points automatically somehow, the game would be more friendly to snipers. Set Your Sights tries to address this by giving some bonuses if you don't move and spend 2 actions to attack, which I think is a nice design.

I think the issue is costing. Mak should cost 2 and Loku should cost 3. I'd play both of them at those costs. But at their current costs I can always find something better.

To me the problem is their health/cost ratio.

Running Mak and Loku together is a 7 point cost. With that you get a tiny 8 HP with a Health/Cost ratio of around 1.14.

Compare this to elite saboteurs, you still get two figures (although in one activation) but now your health to cost ratio is up near 1.7

Other units for reference.:

Reg Sabs: 1.6

Officer: 1.5

Royal Guards: 2.0

Regular Nexu: 1.5

You can see you are not getting a lot of health for your point investment. Maybe this is mitigated if they can effectively snipe and stay out of harms way but with how movement works in this game that's pretty hard to do. Unique characters especially if they want teams to invest into their command deck cards really need to have a substantial amount of health or damage mitigation or they will always struggle to fit on teams. Now maybe if we get some command cards that allow spies to add defense or surge cancels to defensive rolls these guys might see more play. Whenever I am considering them (well at this point Mak + something) I compare them to the elite Sabs.

By choosing Mak/Loku:

We lose one activation but with the latest skirmish rules this isn't a deal breaker.

We lose health drastically and switch from white to black dice. This can sometimes be a boon but has the same odds to be a burden.

We lose the (pretty useful) heavy weapons trait.

We lose the capability to stun/blast (both super useful in skirmish) but gain the option to shoot from further out, in some missions this is okay but we probably want to be close to the action to claim mission objectives etc.

We lose 1 speed on one figure.

You can see here there's very little to gain compared to just bringing the saboteurs. Now if these units were costed at 3 and 2 we now have a Health/Cost ratio of 1.6 and maybe they start to become worth the investment.

To me the problem is their health/cost ratio.

On units as cheap as they are, I'm more worried about total health than health/cost ratio. And at 4 health, either one of them can be one-shotted by any enemy rolling 2 dice. But 5 health (like Gideon has) make a unit much safer. General Sorin, regular and elite Imperial Officers, regular and elite Snowtroopers, regular Stormtroopers, regular Hired Guns, MHD-19, and maybe other figures are entirely incapable of killing a 5-health figure in one shot, unless they are focused.