I think teleporting units should get two things,
One, better behaviour of teleporters when group moving, like when group moving, they will incrementally teleport with everything else they are moving with. This will make them far less likely to teleport way ahead without "backup" and get themselves killed on the offense.
Two, teleporting units are basically specialists at alpha striking, and their stats should reflect that. Thus, a similar transform with damage like space planes got seems to be a good idea.
So despite that these ideas would make teleporting units much nicer to use, it isn't really enough to make me declare teleporters as a potential worst unit.
I would agree with the infiltrators. They have a low HP (which is fine, due to their high ship cap), but thy generally do not live long enough to take qladvantage of their FF immunity. Once again, adjusting their damage stats to focus on "initial volley strength" like space planes seems to be in order, and maybe a light speed buff too.
Armor ships, great durability, ok damage, but it is too slow to really use it, and they don't have enough of the other two to make up for it.
Spirecraft Ion blasters, their currently broken autotargetting behaviour (Mantis issue #4477
) kills it usefulness. Their HP also seems a bit low for their range. So maybe an HP or range buff?
Spirecraft Attrtioners, their base DPS is too low (this also applies to AI attritioners) and having at least some portion of its "damage echoing" be a bit more focused could help make it's effect more visible (relevant forum post: http://www.arcengames.com/forums/index.php/topic,10069
my proposed change to "focus" its special damage "feedback" without making it OP: http://www.arcengames.com/forums/index.php/topic,10069.msg96546.html#msg96546
Spirecraft sheild bearer, a bit of an HP buff and a minimum FF radius would make me happy.
Tachyon drone (the mobile one you don't have to unlock) range is supposed to be small, I know, but right now the range is so small it is useless. And only 2 of them?!
Tachyon turrets, HP seems a bit low for their short range. (not a nomination for "worst" though)
Pretty much all the experimental units I am nominating as well.