all of them is the best answer realy .

It's up to you Chris. I think Cordylines look good as multi stemmed plants. If you want just one stem, cut off the others and just let one grow. There may be a bit of a kink near the bottom, where it comes off the original trunk, but it shouldn't be very noticeable once it gets bigger.

the more you have the more chance that they will servive another hard winter .

Thankyou Noseypotter and Beattie. This was helpful.
Chris

your welcome .