Dry type transformer vs oil-immersed transformer

oil immersed is smaller and quieter, but oil can leak. Oil one also runs cooler as you can make convective oil filled cooling pipe/fins on it.

Oil one has less chance of breakdown due to leakage from water entry.

This is the resource that convinced me that liquid-filled was better than dry-type, especially for indoor installations.
http://www.cooperpower.com/Library/pdf/00006.pdf

Smaller, quieter, more efficient, lower first cost, lasts longer, better overloadabilty, higher transient resistance (BIL), better contamination resistance, better diagnositcs, lower temperature, and ability to integrate primary switchgear compoenents in the transformer. New fluids (vegetable oil based), reduce issues with potential leaks; no fire vaults, and no sprinklers.

Here is a PPT to convey the liquid value to others:
http://www.cooperpower.com/nofires/101reasons.pdf

Not to mention better vibration resistance when used in mobile applications (i.e.- mobile substations).

both the types can have the same shape and size, provided proper insulating material is chosen, for small power application air cooled perform better than oil cooled.

the air cooled are lighter and are readily portable, than the oil cooled versions