Using GPIO to control multiple leds via transistors
Option B is bad because resistor R7 will limit the total current sinked to ground, and that total current will have to be shared among all the LEDs connected to it. Depending on R7's value and the number of LEDs connected to it, the current through the LEDs may not be enough and they won't "turn on", and brightness will be inconsistent (will depend on the number of LEDs "turned on"). Even worse: if you try to select a low value for R7 to overcome this limitation, the current may be far too high when there are only a few LEDs connected, and you may burn them.

Option A is the way to go, as you can limit the LED current individually without any unwanted "interference" from the other ones.