Most of the stock 1.25m and 2.5m LF/O tanks all have a dry:wet mass ratio of 1:9.  Some of the smaller tanks are about 1:5 to 1:8.2.  The KW Rocketry tanks, on the other hand, have usually higher dry/wet mass ratios (usually around 1:10).

SB-4A LFT (1.2x the fuel of the Rockomax Jumbo-64) is 2.12:40.52 or 1:19.1.  It is the most efficient way to move fuel to orbit.  The painted version (SB-4 LFT, also 1.2x capacity of the Jumbo-64) is 4.24:42.64 or 1:10 ratio.

SB-2 LFT (half-size version of the SB-4) is 2.12:21.32 or 1:10.  The SB-1 LFT also has a 1:10 ratio.

The KW pack also ships with a 2.5m RCS fuel tank.  The stock FL-R1 2.5m RCS tank has a dry/wet mass of 0.4:3.4 (1:8.5).  The KW SB-2 RCS fuel tank is 1.2:4.4 for a not very impressive 1:3.7 ratio.