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For surface stations the basic content of TAC and BUFR reports is much the same (there may be higher precision for some variables in BUFR, and there is provision for more frequent reporting) - the main advantage of BUFR is the provision of extra meta-data (such as height of temperature and wind measurement and instruments used). For land stations there is explicit inclusion of position information (which has both pros and cons, see Meta-data page). Note that there are several different BUFR templates for "SYNOP" data (and that values can be set to missing) so particular meta-data items may not be available for all stations. The work on marine BUFR templates and reports is at an earlier stage than that for land stations. (Note that METAR code will be replaced by an XML based code: ICAO Meteorological Exchange Model - IWXXM. This is outside the scope of these pages.) For radiosondes there are more major changes to report structure - all levels (either up to 100 hPa or up to balloon burst) should be reported together (not as separate "Parts" for standard and significant levels). For some stations there is also a move to reporting of high resolution data (eg every two seconds during the flight) which can result in 5000 or more levels compared to 200 or so for TEMP code (all parts combined). For some stations/templates there are more meta-data and also position/time information for each level which should facilitate more accurate treatment of radiosonde drift.
A poster on the status in early June 2014 and ECMWF plans is available at UEF2014 presentations (pdf, ~10MB).