Depends entirely on what you want.
Personal opinions:
Tactician has the best resist pool allowing easier capping, and high potential crit damage. You don’t even need to push base OA that high, you can rely on Markovian’s Advantage Debuff then fighting spirit proc to proc Deadly aim and suddenly you’re critting like gangbusters in bursts of 5 seconds out of 16. An extra source of flat damage absorb can be amazing, or used instead of menhir’s bastion and take conviction or olerons. It also has pretty solid itemization support. Since you mentioned forcewave tactician you’d really want to try to go oleron’s for the extra flat trauma, since stacking trauma and the octavius set is pretty obviously going to be sweet.
Witchblade, however, has, in my opinion, the best offensive potential if you’re ignoring non-soldier itemization. Zero extra skill ranks and CoF is still a great force multiplier. (okay, it’s a x1.27 multiplier, but that’s still surprisingly good, especially combined with rank 12 or so Break Morale giving another 30 reduction). Likewise bang for your buck Blood of Dreeg even with no extra ranks is an excellent buff that synergises well. Health regen, OA, phys resist. All things a heavily defensive build can always use more of, with the CoF providing the extra punch that sort of build can be lacking in.
Commando: Blast shield. That’s really it. The flat damage and damage bonuses don’t really matter much, unless/even if you’re gearing heavily into demo +levels. Vindictive Flames damage proc by itself is okay but not particularly amazing unless you’re intentionally trying to gear for it. Flashbang if you’re doing some kind of glass cannon maybe?
Aether DK is basically exactly one set of gear. It looks great, with a dedicated full set support and a couple of weapons/shields options depending on if you want to chase blue text or aether damage. Great resist reduction options. However, the exact same gear that makes it at all possible also means you aren’t taking the soldier gear that usually turns a soldier mastery class into an unkillable killing machine. Necro has some pretty nice defensive skills, but it’s going to be way more offense oriented in my opinion. Probably more than sturdy enough, even a couple of back to back stuns/freezes will pop menhir and then you panic pound the mark of torment button so it goes off soon as you break free of cc. That should give you enough time to get siphon soul back up (if relying on it) or just smack something enough to life leech back up.
Retaliation Warder, ala the Avenger of Cairn build that has a thread here is probably the strongest, though. Other than retaliation, though, no one needs to be THAT unkillable, and the other combos synergize better for offense, imo. Especially S&B.
Battlemage: Same gear as the Aether DK, trades resist reduction for another nuke or two in callidors/devestation (subbing spellscourge shield). Sometimes you just want stuff to blow up. Also with a second source of %damage absorb I feel like it gives a less spiky defensive curve than the DK version.