Hi there, I was wondering what defense you think is the most appropriate for a team that has a group of forwards-centers that are medium in size and not fast enough to play man defense at their current level. Guards are not a problem, they are OK and even matched with most guards on their league. Any thoughts?

How old are they? How often do you practice? What are your primary goals? Win. Develop players for the long term. Both.

20's, 5 times a week, both

I'm not sure there is a best defense. It's not so much "what" you run but "how" you run it.

What defense are the players used to? Do they have strong man to man defensive fundamentals and understand the concepts?

You can make a man to man, zone, or match up work because all those defenses can be adapted to your personnel / player strengths. It just all depends on how well you teach the defense and adapt to your team.

Now if I didn't have any depth and had to run with pretty much 5 players, I might go to a zone. Here are some pros and cons to zone:
http://www.coachesclipboard.net/ZoneDefense.html

However if developing the kids for the future I might go with man to man and really focus on teaching those good fundamentals. Personally I always teach man to man. And I think that's what is best for youth players. But with older players there are other good options to consider.

I think the big key here is to TEACH good help defense... regardless of whether you play m2m or zone that is the key to play a good D! JMO of course.

If your guards are good you can play them to their strenghts and sag the bigs so they are in a good help position.