Short or tall?  What looks best?  If that was all you had to consider, when landscaping your property....well....it would be easy!  Not today - at least, in the "post 9/11" world that we now live in...  Why would landscaping have anything to do with neighborhood watch?  Think about it - you CAN'T PREVENT, WHAT YOU CAN'T SEE....For example, if you have bushes and shrubs close to your house foundation - especially in front of window openings - you may be inviting intruders to take advantage of same as ingress and egress points, during home invasions.  Especially, if your plantings are VERY TALL, AND HELP TO CONCEAL ACCESS POINTS INTO AND OUT OF YOUR HOUSE.  It is best to keep the plants and shrubs below the lower window sill level...REMEMBER - YOU CAN'T PREVENT WHAT YOU CAN'T SEE!!!