I think it is a question of what you use them for. RT is a great package for stock trading and pretty stable although certainly not problem free. QCharts is great for a multimonitor setup if you like to watch a lot of stuff like tick and trin because the cursor tracks on all charts. For me that is a huge feature and makes QCharts a great package for daytrading the e-mini's. QCharts has issues from time to time, although it is definitely more reliable than it used to be.
I do agree with metoxx's observation though. Cost really should not be a primary factor.