Whats the difference between these three breakout boards for the ADXL345 Accelerometer?
As you've figured out, these boards all do the same thing electrically.  The relevant pins of the part are brought out, as well as the manufacturer-recommended grounding and bypass capacitors.  (It would be wise to read the datasheet and double-check these yourself.)

If you are going to use the ADXL345 on a multiplexed SPI bus, you need an additional logic gate.  See the datasheet or previous discussion: https://electronics.stackexchange.com/a/34586/411

One consideration unique to accelerometers is their sensitivity to the mechanical mounting of the circuit board.  If you mount only the edge of the board it can resonate like a tuning fork and affect the measurement.  Or if you mount it with something like foam tape it can absorb high-frequency vibrations, for better or worse.  The datasheet has a section discussing this.  So maybe the choice of physical mounting arrangement will lead you to choose one board over another.