Jesus people, you need to get out and play more. Have any of you seen Festung Armor in a competitive game at even a semi-decent level used successfully? Me neither.
OKW Pak 43 is more viable for two simple reasons: A, you can build it next to the Schwere Panzer Headquarters, and B, OKW fortified, unlike Festung Armor, will not preclude you from getting heavy armour of your own. I've played quite a bit of OH 1s recently (sometimes I feel masochistic) and the IS-2 is a major problem. Just about the only thing that effectively neutralises it is the Ele. However, an Ele is not gonna do much ie. on Semois/La Gleize/Stalingrad etc. Tigers with Paks/Tellers are the next best thing and can contain it, but they are by no means reliable, the IS-2 with its ridonculous frontal armour is just more survivable and a good deal more effective in terms of anti-vehicle capability.
Tiger can't really do much most of the time to is-2 even with pak support.is-2 plus zis beats tiger-pak unfortunately.
Pak43 works well vs is-2 in bigger gamemodes,but not 1 vs 1.Panther-elefant are ur primary hopes.
Riegels are useful.
I like double or triple packing tellers if using muni conversion doc or floating lategame.