I wanted to objectively determine the best way to reach all parts of the Milky Way galaxy using BT technology (think long-term reliability).
For this I selected two criteria: cost per person and tonnage per person. Keeping the former low is important to get such an enterprise off the ground, while the latter reduces the industrial burden on the decedents for making additional additional ships (to house population growth and other reasons).
To calculate the best setup I compared various combinations (DS, JS & WS) with standardized stats (same armor type, SI value, ratio of cargo/quarters, etc). [I had also considered Space Stations with KF booms as an option, but the answer to my rules question makes it clear that they aren't a viable option for this scenario.]
The results clearly point out some facts, bigger is always better and that the DropShips cost multiplier is a killer.
Cost-wise a JumpShip fully loaded with ten 100k DropShip scores only average on the list of combinations, while 2.5MT WarShip with no DropShips gives the best cost per person. This can be demonstrated using mostly canon ships. Here I am assuming that half of the cargo (including all the yard stuff and escape pods) will be used for additional steerage quarters. So a Monolith & 9 Behemoths vs a stripped Newgrande & 4 Behemoths.
Monolith (habitat)+9B: 68257P 26.5B 1330kt = 388,239 CBill/P & 19.49 Ton/P
NewGrange (habitat)+4B: 119709P 29.71B 2700kt = 248,185 Cbill/P & 22.55 Ton/P
Now compare those to somewhat optimized custom designs to how far it can be improved.
Cluster JS & 10 Island DS: 88839P 30.07B 1455kt = 338,477 CBill/P & 16.38 Ton/P
Sunflower ColonyShip* (0 DS): 111115P 16.12B 2500kt = 145,074 Cbill/P & 22.50 Ton/P
Canon ships are pretty decent, but custom designs can really get some real gains, however the existing facts don't change. Using a JumpShip gives a noticeable mass advantage, however using a compact-core ship (WS) cuts the costs down by more than half. This does suggest to me that the 'Single WS' set-up is likely the best technical solution, but we all know that most factions will not be able to build such large ships. But personally I can see something like it being commissioned by DOME (Department of Mega Engineering, from the first Star League).
ps. [TPTB should really look into a separate cost multiplier for non-atmospheric DropShips, so some errata please.... pretty please... ]