John, There are many types of juniper.There is everything from Alligator,Oneseed,Utah,Western,California and Rocky Mountain just to name a few. The variences can be very different in quallity and strengths and but physical apearence is often very subtle. Often just the needle like twigs being 1/32 or 1/16 difference. One tree can have wood like balsa wood and the next as strong as yew. Rocky Mountain is generally the strongest but also is often the most distorted with knots everywhere.
Common juniper can be good or bad depending on location. I have found the trees with more of a pale yellow heartwood to be weaker and the trees with darker orange or reddish heartwod to be stronger. I also believe the top side of the branches to be better then the trunks of a tree.
BTW I did make a bow out of the branch from the rondevous. Had it near finished and tillered, even shot several hundred times but I kept taking the tips narrower and narrower to try to get those extream needle tips and finally had a tip let go at 26" on a 48" bow. It snapped back so hard that it broke the belly of the handle section.
I have a good book giving the types and what to look for but it's teadious reading. I'll try to narrow it down for you tomarrow