It's so difficult to predict bus service... you can have 2 families, in 2 different parts of the resort, on 2 different park schedules... and they can have 2 completely different opinions on bus service.
The biggest difference you may notice... is that POR has 3 internal stops, compared to CBR's 7. In theory, it makes POR seem like the top candidate... but if you're traveling to any other park besides MK, expect an additional stop at POFQ as the two resort share a bus stop.
After 4 trips at CBR, the overwhelming positive reviews of POR lead me to book it. Perhaps it was over-hyped, or my expectations were set to high... but the resort was a huge disappointment. The awkward layout (we were in Alligator Bayou) the simplistic theme, and the overall feel of the resort just wasn't for us.
I longed for my vibrate colored villages complete with their own quiet pools and bus stops, the tropical lush landscaping and sandy beaches lining the lakeside, and an atmosphere that led me to forget I was even in WDW. It's even more tempting with the recent room renovations and expanded pool deck to include a splash playground for small children, a feature no other moderate currently offers.
We've had great service at both... and know to expect long lines at park closings. The bus service wouldn't be a deciding factor for us... as it's all just a matter of personal opinion and experiences. Again, the 3 (or 4) stops at POR is certainly less than the 7 at CBR... so that's absolutely an advantage for POR.