There seems to be two kinds of housemates
 

The arguers - these people are paranoid, on edge and ready to argue about anything. These are Nicola, Spencer, Callum, Kim, Stacy

The chillers - they are too relaxed and sensible to get into unnecessary arguments. These are Colleen, Jedward, Jamie, Bianca, James C, Jessica

Heidi is one I'm less sure about. I think as an individual she's a chiller but being loyal to Spencer, she follows him into unnecessary arguments.

Of course I'm basing this on having not watched all the series in full.