your needle size is dependant on the weight of the thread you are using- you need to use the correct size needle for the thread to keep from having stitch problems-breaking thread- ect.
if i am machine piecing i generally use a 40 or 50 weight thread
if i am hand piecing i tend to use 100 wt silk thread...sometimes a 60 weight something else.
i use 'sharps' most often for type of needle- in the size needed for the thread i'm using.
i purchase alot of my thread from connecting threads- some from Superior Threads-