Hey Zappa,
Procumbens nana has been a favorite of local clubs across the country for years. For a more upright variety, San Jose juniper has also been a fave because of their rugged trunks. For some reason, although it has beautiful foliage, Hollywood juniper doesn't seem to take to bonsai culture very well. Others may have a different take on that one, but that's my experience here and what I hear from others including Boon.
PM me if you get a chance!