Has anyone any advice to give as regards multi fuel/log/gas fires.
Which one would be more suitable for a finca, we have a chimney.

Thank you.

Best advice is both. The log burner will nicely heat one room if it is big enough.  What about the other rooms ?
We started with a stove but after a few winters added gas fired central heating. The problem with the stove was no distributed heat and it tended to be almost out in the morning. The luxury of being able to wake up to a warm bedroom and bathroom were worth the expense. I get thro' a bottle of gas in 7 days on average during the winter. We still have the stove lit in the evenings.

The best advice I recieved some years ago regarding log burners was that if you use one infrequently then choose a steel one as it can handle multiple cold starts and heats up quickly. A cast iron one needs to be heated gently and is better suited to regular use as it retains its heat for much longer.
In both cases expose the chimney flue to the room(s) as this is where the bulk of the heat goes!
You can get a thermal fan that sits on top of a wood burner that spins faster as it gets hotter therefore pushing warm air into the room...... and finally....I was told to throw a 2kg bag of salt onto a roaring fire once a year as it clears the flue of tar and resin which can be considerable if you burn pine logs.
Hope this helps