what do you usually put on tie bombers and why?

Bombs of various sorts, because they completely and totally outclass missiles and torpedoes.

Other than that, it really depends on what you intend to do with your squad.

Either Proton Torpedo or Concussion Missiles. They're both 4 points so the points seem to work out well. Concussion missiles are slightly better against unshielded craft, so sometimes it's good to mix and match.

But with the Transport and Wave 4 coming out, with 2 point Flechette Torpedoes and 3 point Ion Pulse missiles, what you can load on a bomber is due to change drastically.

which is better concussion missile or cluster missiles? or does it depend on your targets agil?

also aren't ion pulse missiles just 1 shot target lock burning ion cannons for equal cost? If I'm not mistaken imperials don't yet have small ships that can use them but if/when they do have one wouldn't that be significantly better unless you wanted HLC or some other cannon instead?

Nevermind... I missread the question. Vorpal has the correct answer below.

which is better concussion missile or cluster missiles? or does it depend on your targets agil?

I would only run Cluster Missiles if I have Jonus to help the attack. With B-Wings being so popular they aren't a bad option, but Concussion Missiles are more consistent.

Clusters need modifiers for both attacks to be useful, and so are useful only with Jonus, Marksmanship, or Recon Specialist.

However, Cluster Missiles aren't good enough to warrant Marksmanship, and Recon Spec's superb regardless of your ordnance. Concussions are far more consistent in any non-Jonus fleet.