Bombers. Resistant to flak and still deadly to lrms (not quite as much as fighters) The idea being however, you must take down the lrms numbers so you can get at the flak with lfs. Most likely your opponent will start building more flak to kill your bombers, thats when you dockem and send in the lfs to start shredding some flak. Its tricky but manageable. just make sure you use your bombers and your own lrfs to drop his lrf numbers. Additionally setting your bombers on hold position will keep them alive longer. Simply set them to hold position and then move (do not issue an attack order) close to what you want them to kill. 9 times out of ten theyll automatically attack their nearest target when they move to the position youve set for them. Also remember that LFs are faster than lrfs, if you can bait his lrfs out of the protection of his flaks by skirting the well with a group of lfs, you'll break up that nasty combo and your bombers/fighters will have free reign to blow those lrfs out of the sky. Once the lrfs numbers are down, dock your bombers in the carriers to preserve squadron strength. When he realizes hes too low on lrfs to pummel your lfs he'll start rebuilding them. Thats when you launch again to keep em down while your lfs clean up the flak.
Best thing you can have in this situation is a balanced fleet. Get some bombers, flak, lrfs and lfs. Keep your bombers docked if their are any fighters in the area and use your own flak to thin them out before launching your bombers. Lrfs bombers and flak on his lrfs. Then charge in with the lfs.
If you can surmise that your nearest opponent is contructing lrfs and flak early, you can start building carriers early and loading them with bombers (the first 1 or 2 you build load with fighters so when he scouts you thats all he sees, and he'll feel delighted that hes already got you cornered with his flak) Then the rest go bombers and keep em docked. This way you can surprise him and maybe even be able to take out his Cap ship before he realizes his mistake. 8-9 squads of bombers will shred a low level cap with surprising speed. After a decent amount of carriers, go lrfs lfs and flak.