I have some experience here:
1) Poland: Poland is easily defensible for Germany and is relatively high in the IPC count. Also, it is low enough in the IPC count that it’s not valuable enough to be SBR’d by England/America if you put an AA Gun there. (Do the math, you’d expect to lose between 2 IPC and 2.4 IPC per round to do 3.5 IPC in damage. Not a stellar use of that bomber, eh? Not when you can bring it into a battle to kill a defending infantry that costs 3 IPC and costs the enemy the opportunity to use it against you later. Note: Some like to determine the loss of the bomber over 6 rounds {2 ipc/rnd} some over 5 since the bomber can be considered lost on the 6th {2.4 ipc/rnd} so I listed both.)
2) France: Aweful! Yes, it’s worth 6 IPC so you could build 6 units there. BUT! 16 Infantry = 48 IPC, therefore, if you want tanks and artillery and ships and planes, there is strong odds you won’t use the full capacity of your two territories (Germany/France). On top of that, it’s an extra space away from Russia. Are you going for Moscow, or Washington DC? Worse still, you put an IC in France, I’m going heavy on the bombers because I can now do 32 IPC in damage to you each round.
3) Bulgaria: This has worked for me, but lately, people are getting smart too it. It’s nice because it’s closer to Caucasus and because Germany has a hard time getting units down there. It’s bad because it’s not adjacent to either Germany or Italy and thus hard to reinforce.
4) Norway: This has worked for me as well, good way to keep Russia from getting the big NO, but you really have to dedicate yourself to keeping it out of the hands of the allies. It’s been distracting sometimes.
That said, honestly, I’ve been moving away from German complexes. I like the following:
Japanese Complex in Sumatra
Japanese Complex in Manchuria
Japanese Complex in Burma
Italian Complex in Egypt
Italian Complex in S. Africa
Italian/German Complex in Brazil
Note, I don’t mean to build ALL of those complexes, but those are the territories and nations I tend to build complexes in.
America could have one in Brazil, Norway and/or France. Even put one in Philippines and Hawaii once.
England could have one in S. Africa, India, Australia and/or Egypt, France, Norway
Russia could have one in Poland, Bulgaria, Novosibirsk
Again, not ALL of them, and not necessarily early in the game, could be towards the end, but definitely as needed given the position on the board!