I think that HLCs are 100% the way to go. I feel like the loss of the die is just terrible. HLCs are still good against fatties that crits would otherwise be nice for, but Manglers are terrible against high AGI token tankers that HLCs can handle. I tend to have high AGI in a lot of my lists, and if I see a Mangler instead of an HLC, I'm a pretty happy camper.
The Advanced Sensors vs FCS is an interesting problem, because they're both so good, and IGs can make such good use of both. I'm tending to lean toward FCS (in that I would rather not face it), because of the relatively low PS of IGs. Advanced Sensors ends up being less good (although certainly not useless) if you have a lower PS, but FCS is pretty much always good. FCS leaves just a few extra points for a bid or Inertial Dampeners or whatnot. It also means that stress as a weapon doesn't leave you without offensive boosts. I feel like Advanced Sensors loses a lot if things Go Wrong .