Which Company/Website do you use and think is best to do stock trading?

Hey mates, was just wondering what you guys think are some of the better companies to trade with. Would you recommend doing it through a major bank like RBC or Scotia iTrade, TD Waterhouse, etc. or through a stock only company?

BTW, I'm just a beginner.

I'm signing up with RBC Investments today and using their practice accounts.

How do you guys shelter your profits you make from taxes? Through RRSP account or TFSA? TFSA I believe is 10k limit right?

What I don't get is why you would use RRSP when you still get taxed upon withdrawl? I guess you want to use that money that would be taxed as more investments?