The Pi I am using is the Raspberry Pi B+. The advantage of having this particular version of the Raspberry Pi is the upgrades from previous version the Raspberry Pi B. In this revision the amount of USB slots has been increased from 2 to 4 giving you greater flexibility with the number of things you can connect to the Pi. The number of GPIO pins has increased from 26 to 40 pins giving the user the ability to give the Pi more options to sense and control more things. The addition of the Micro SD card has given the Pi a greater form factor, reducing the level the card sticks out from the board which in turn reduces the chance that the card will be knocked out or damaged. The audio circuit has been upgraded with a low noise power supply to improve the quality of the audio out with the 3.5mm jack.
At the present time the Raspberry Pi B+ has been superseded by the Raspberry Pi 2. The Raspberry Pi 2 is an exciting new extension to the Raspberry Pi family, with higher specs that basically bring it up to date with tablets and phones. It will be interesting to see how far it will drive future projects for makers. I will continue to use the Raspberry Pi B+ as for the moment it is adequate for what I need.