Wow--they are both great times! We are great fans of February, as we live in Pennsylvania, and we love to get out of the cold weather. This is the third year we will be going. The parks weren't crowded and we were able to get right on the attractions in which we were interested. It does get cold in the mornings and evenings and you will need a sweatshirt and a jacket--basically, layer yourself, as you will find yourself in short sleeves in the afternoon or maybe even sleeveless. Beginning of February, first week, is cheaper, and then it gets more expensive starting the second week.
October is mid-range prices and also a great time, getting the warmer weather and longer days! It is definitely better if you want to do the water parks.
Five days is fine if you doing the 4 parks, but if you also want to do the water parks and all Disney has to offer, a week would probably give you more time to get it all in without rushing around, especially if you have real little children.
Have Fun!
Sandy