I make my decision on how to heat (Ceramic or Furnace) based upon who is paying for it.. Normally, I do not pay for electricity (Included in site) so.....
If you are paying for it there is a formula.. Someone can tell it to you.
If you are not paying for shore power: Ceramic heater
IF you are paying for shore power: Compare Electric Blanket to Propane furnace
NOTE that furnace may also heat water system to prevent freezing.
IF you are BOONDOCKING... things get complex. because you have to figure out the cost of the Generator for recharging the batteries to heat that blanket.
Also as Jim and Ned noted.. Many electric blankets have been totaled by MSW inverters..
Regarding inverters in general: There used to be a rather long document on Xantrex's web site "Things that might not work properly on MSW inverter power" or some such title.. INcluded Electric Blankets, LED night lights and a lot more stuff, All manner of audio/video/radio gear (Televisions for example) timers, digital anything....
No such list exists for True Sine Inverters.... because the only thing that wont work with them (Applies to MSW as well) is "Devices needing more watts than the inverter can produce"