Pressurized suspendium is the best source of armored lift at the moment. First of all it's straight up the cheapest. Lets compare the the surplus lift (lift - weight) to cost ratio of pressurized suspendium, the medium chamber, and the large chamber.
Only considering module, armor costs and weight, the ratios rounded to one decimal are:
med steel hvy wood hvy steel
pressurized 6.8 6.7 6.2
medium 4.8 4.5 4.1
large 6.0 5.9 5.5
Accounting for the costs of 3 years of crew and coal maintainence, along with some costs for supporting modules (enough coal for 3 mins, 3 years of coal and crew costs, +20 cost to represent some solid shapes for pressurized), the ratios become:
med steel hvy wood hvy steel
pressurized 6.1 6.1 5.5
medium 3.9 3.9 3.6
large 5.2 5.1 4.7
There is also some harder to quantify benifits to pressurized suspendium:
- more lift modules to destroy
- infinite up time
- no crew
- no coal
- placable far from important modules to avoid explosion damage on destruction
- no smoke stack like the large chamber
Despite chambers being way harder to build a ship around they are more expensive than pressurized suspendium. Balancing hazardous and cheap suspendium chambers and safer but more expensive pressurized suspendium seems like a more interesting dynamic than adding pressurized suspendium until you have enough lift.