I still have difficulty believing defensive could be better than offensive. Maintenance cost doesn't translate that well to bigger armies if you're already at your forcelimit, and it doesn't even come close to a straight +20% forcelimit bonus. +1 AT certainly doesn't feel superior to +1 shock/fire either, but I could be wrong. Morale and Discipline both have advantages over eachother at different stages of the game, and I'd trade a lot more attrition buffs than defensive gets for a straight +20% siege ability. That doesn't even account for forced march, which is still incredibly useful.
When is 20% forcelimit that great really? Sure it's good. But great? No.
Early game, what good is 20% FL when you only have 10... 2 more infantry units isnt going to do much for you. Late game, I'm rarely even at my forcelimit, let alone above it. And if I am above it, it's because I'm fabulously wealthy and could care less what my actual FL is.
+1 shock/fire? Ok these I'd call great... but greater than 15% more morale? Nope.
20% siege ability isnt 20% faster seiges. Nope. Guns have more impact than that idea. And guns are expensive without things to reduce that cost.
I'm not saying take ONLY defensive... you should still take offensive as well. But get defensive first (as your second idea set). It's bonuses are more helpfull early game, when you really need them. Offensive's power is more useful when your big and powerful and simply want to take on other big powers quicker. Defensive in the early game (when seiges take 3 or 4 years) is a must have or your manpower pool will never recover from the constant attrition.