It really depends on your stat budget as to how much of each you want. I will say though that most comms purchaseable gear is either shield/absorb enhancements or defence/alacrity or defence/accuracy. Shield/Defence seems to only come from drops or maybe the other tank classes gear which is really painful. As such I tend to be grabbing Defence wherever I can and only using Absorb where I'm forced to. Similarly, I'll be augmenting for Defence entirely.
I think I saw a good mod on the belt which I plan to purchase a lot of. I am also probably going to augment with fully defense augments, thankfully I am synthweaving!