I am currently thinking about changing defenses on one of my teams...  we are losing 7 seniors this season, have 2 returning junior's and the rest are freshman.... would this be the best opportunity i'm going to have to start switching over to the full court press?

I'd say so. 

I took over a new team this year with 7 open scholarships, and I switched from man to press and still made the PIT. Practiced press all season but played man for non-conference and switched to press for conference play. 

interesting....   did you use 20 practice minutes or what

20 practice minutes. I had pretty much written the season off as a loss, but I ran the old defense while playing my upperclassmen during non-con to try to help the conference RPI. Then in conference play I bumped up my freshmen minutes and switched to the new D, and I actually (surprisingly) got better. I guess by that point the seniors were at C+ or B- in the press, and so I went from having 5 players who knew the D really well and 7 who were awful to 12 who were around B-. In a press, I guess the latter is better. 

is the press in your opinion the most affective defense?

I don't know. I have a bunch of teams, but I'm only in my 5th season with the team I've had the longest. I just already had a flex/man team and took over another one. Because flex supposedly requires more speed than triangle and motion, I figured it'd be logical to pair with the press. Right now, I have two press teams, two man, and two zone, and I'm still figuring out the strengths and weaknesses of each. 

The press is the easiest to run, in my opinion. I've heard some coaches complain about the press at the very upper levels of this game because it can produce inconsistent results against very good teams, however, if you're an up and coming team, the press is the best way to play above your head.

Also, the general consensus is the best is press, 2nd best is man and worst is zone. Not that they can't all be run very effectively.