It depends on the offense that you will face and the type of athletes you have. A lot of freshman teams don't have developed WRs or a QB that is consistent, and therefore rely heavily on the run. In this case, something like the 46 Bear would be good to stop the run, but again you need the right type of personnel to run it. A lot of high school teams are starting to run the spread now as well. From what I have read and seen defenses with a 3 man line (3-4, 3-5, or 3-3 stack) are most successful against spread option schemes. An odd front may also be effective for schools that do not get big incoming freshman. This type of scheme allows you to put more of your smaller, more "athletic" kids on the field as DBs or LBs. Bottom line though, to run any scheme, at any level, you have to have the right types of players to fit it, and you should take into account the types of offensive schemes you will be defending.
I agree with joebye it is difficult for varsity coaches when the freshmen and jv levels run a completely different defense. The longer the kid is in the same system the more comfortable they will get and the faster they will be able to play at the varsity level.
This is one of the reason's why it is harder to be a lower level coach. You get what is left over and you have to coach them up. Do what the head coach does but you should also be creative. If you are getting killed in a 3-5 why would you stay in it. We are also trying to develop young men to play football. they should know more than one thing.
For all the years I was an offensive coordinator at the high school level I would really let my frosh and JV coaches be creative. You can apply this to defense as well.
I have a set of athletes that I have to create an offense around and they do as well. If I have a great QB and mediocre running backs for my level then I'm obviously going to want to pass the ball more. If the frosh and JV teams have mediocre QB play and very good backs for their level it would be ridiculous for me to ask them to follow what I do.
So, what we would do is work inside the parameters of my offensive playbook, but apply the certain areas of it to the particular athletes. It really allowed for the younger guys to get better and when they came to my level I would incorporate their game into the offense. So they know the playbook, but at the same time they've been doing what they're good at for their entire career by the time they graduate.
There are a lot of head coaches and coordinators who get stuck in their ways and make kids adapt to them. In my opinion it should be the other way around. I'm not the one that's required to make plays, the kids are. If you can get the same type of athletes year after year after year then fine, but that's very rare in most cases. With AZ's pillow soft recruiting enforcement rules you can be a strict scheme coach and still win at a high rate.