I have maxed HTs and I play with all HT combo in MP and WW. I was Roman and now I'm German.
MP attack (raiding) looks like this: Choose a weaker base preferably with triggered traps. Deploy HTs all around the base, then snipe AT guns with your fighters as the HTs come close to them. Nothing can stop the HTs from destroying the base. You will have zero loses. Romans are slightly better then Germans in this scenario because they can field 7 HTs instead of 6, and they do not need to take care about Fury bonus management.
WW attack looks like this (considering though opponent): Deploy all HTs at one corner (the one that has less AT defenses), then Deploy TDs and generals in the second corner, then deploy auxliary force (Terra Cotta Army, Alliance Howitzers and shooters, Coalition troops) the the third corner (the one with more ATs and less mortars). Optionally you can deploy TTs in the fourth corner to get quicker destruction. As your forces come closer to the center, deploy blitzkrieg tactic, try to snipe any dangerous AT guns with your fighters, and place as many Decoy tactics as needed. Germans are much better then Romans in this scenario, because 6 HT in one group are sufficient (one more HT makes no difference), but all units (especially fighters) have Fury bonus (+15% damage), which makes an edge against well fortified opponent.