Just put Arcane Shield on a clamjack and let it contest until the end of time. Arm 28 tends to be tough to kill on anything.
ARM 26, 31 on Feat turn (is that a new record btw?) - remember Clamjacks went from ARM 25 to 23 in the transition to MkIII.
Centurion is ARM 24 (and his armour is easier to circumvent with chain weapons etc), but hits harder and his ARM doesn't drop by 4 if he attacks, plus of course doesn't have immunity to pushes, so he's not as good a zone holder but can contribute more offensively. So I think both have value. Of course it's just fun to get to say something stupid like "my model is now ARM 31".
On the other hand getting past Arcane Shield isn't as hard as it used to be...