Rails are king right now. If they're good with them, a full LR rail wing is probably the most dangerous thing out there. LR is stupidly OP right now - why they made the range out to 6k is beyond me... it just promotes lame tactics. SDC's 3PA/2 rail is king for maintaining alpha dps under focus, I just explained that elsewhere in this forum so I'm not going to repeat the why's of that.
If you run heavy on rails, make sure your whole wing does. You will likely be first focus if you're any threat with them.
If I ran a FAS, which I haven't for over a year because it messes with the feel on the fdl for me, I would probably TLB PA the top c3 and run 3 rails on the bottom. But I prefer rails over pa's and don't mind giving up a c3 or even c4 slot for them. Most seem to go pa's on the bottom shelf, if not full pa's. Go watch some of the following people's vids: monstro99, ryan_m17, pelucheuh, and beumer. That'll be a good general capability guide on the FAS.