@LaraUS: korrekt ist "m²", und zwar mit Leerzeichen zwischen Maßzahl und Maßeinheit. Beispiel: 234 m².

Is there any difference between the two in this context?

Oxford Style Guide:

sq. m. = square metres (not used in scientific and technical work)

"ha=hectares; sqm=square metre; sqft=square foot " http://www.chichester.gov.uk/documents/upload...

"Redevelopment to provide 28566 sq.m. " http://www.london.gov.uk/mayor/planning_decis...

In the art texts I have translated (catalogues, press releases etc)I have been told to use m² as Chris recommended. Perhaps sqm is more common for town planning (or other non-arty sources), in keeping with the links provided by CM2DD? Or maybe it really is just personal preference.

My guess would be that it may be more for more prgamatic reasons, like typesetting & problems with superscripting the 2. Or perhaps sqm is intended to be easier for non-mathematicians t understand.