Plottman:
I recommend buying each style of turkey call out on the market and just play with them. This allows you to choose which call style you like best.
When it comes to the best time to call a bird in... Well I would say any time is a good time. Thats where scouting comes in and knowing the birds your hunting... I personally have had the best luck in the 3rd week of the season to call birds in but I have friends who call them in opening day.
Good luck!