My favorite area to watch the parade from is the taped-off area near the Tusker House entrance/Dawa Bar in Africa. If it's rained recently and tape isn't sticking, ropes go up instead of tape, but it's still a great spot! Get there between 3 and 3:30 depending on how busy the park is and your party size.
Otherwise, I like anywhere near Tamu Tamu or the popcorn cart in Africa where the turn to Asia is. As a general rule, the closer you are to the rope, the better view of the parade. These areas tend to fill up between 3:10 and 3:40 depending on crowd levels.
In general, the Jammin' Jungle Parade isn't extremely crowded. It runs in enough space that there are plentiful places from which to watch the parade, and a lot of the time, a lot of AK guests don't watch the parade (there is a showing of Nemo always running during the parade, and when FotLK was running, there was often a show just before or during the parade). Usually, Africa fills out the good spots between 3:15 and 3:30 depending on crowd levels. Assuming the parade starts out on time, it usually gets to Africa somewhere around 4, since Africa is pretty much the end of the parade. I love to watch it from there--it has a lot of very desirable spots, but in general they don't fill up till 30-45 minutes till parade (which is fine for me, your mileage may vary).