That's entirely up to you and your preference on the way your plant looks. If you don't like the look of multiple stems cut the extras off. I usually wait until they are big enough to root and sometimes you will get a sport that has foliage different then the parent plant though that is rare.

Karyn said it all. A single stem will give you more of a tree-look. My oldest brug has three stems and it is very pretty that way. Makes the plant look fuller.